C#: tests in CI are disabled

In https://github.com/bytecodealliance/wit-bindgen/pull/1699 I'm disabling testing with C# due to failures building tests.

An example failure with wasi-sdk-29 is [here](https://github.com/bytecodealliance/wit-bindgen/actions/runs/33020711410/job/98363825803):

```
---- tests/runtime/rust/dylibs/runner.rs ----
component: runner
path: tests/runtime/rust/dylibs/runner.rs
error: failed to compile component "tests/runtime/rust/dylibs/runner.rs"

Caused by:
command execution failed
command: BINDINGS="/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/dylibs/runner-rust/bindings/runner.rs" CARGO_MANIFEST_DIR="tests/runtime/rust/dylibs" "rustc" "--edition=2021" "--target" "wasm32-wasip2" "-Dwarnings" "-Cdebuginfo=1" "-Ldependency=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/debug/deps" "-Ldependency=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/debug/build/quote-53a208424db1e1d7" "-Ldependency=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/debug/build/serde_core-0ecc340f22280655" "-Ldependency=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/debug/build/proc-macro2-6955ed29c3acce69" "-Ldependency=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/debug/build/anyhow-ce8ecf614e24fd86" "-Ldependency=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/debug/build/zmij-5e4b739506ce1fa0" "-Ldependency=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/debug/build/serde_json-2bddfa072642257e" "-Ldependency=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/debug/build/serde-8c4981138e2ed61c" "-Ldependency=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/debug/build/prettyplease-3bdb7e6f3ad61c08" "-Ldependency=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/wasm32-wasip2/debug/deps" "-Ldependency=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/debug/build/wit-bindgen-rust-ea4e7d82dea7c074" "-Ldependency=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/debug/build/wit-bindgen-rust-macro-b2978fab7bdd55a9" "-Ldependency=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/debug/build/wit-bindgen-a11e78330ba53fc2" "-Ldependency=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/wasm32-wasip2/debug" "-Lnative=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/wasm32-wasip2/debug/build/wit-bindgen-41a5941b58e7a593/out" "--extern=wit_bindgen=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/wasm32-wasip2/debug/libwit_bindgen.rlib" "--extern=wit_bindgen=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/wasm32-wasip2/debug/deps/libwit_bindgen-83c4ea851fcc31f6.rmeta" "--extern=futures=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/wasm32-wasip2/debug/libfutures.rlib" "--extern=futures=/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/wasm32-wasip2/debug/deps/libfutures-b27c7f5ef205c54f.rmeta" "tests/runtime/rust/dylibs/runner.rs" "-o" "/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/dylibs/runner-rust.core.wasm" "-Clink-arg=-shared" "-Clink-self-contained=n" "-Clinker=/opt/hostedtoolcache/wasi-sdk-29.0-x86_64-linux/bin/clang" "-L" "/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/dylibs/runner-rust" "--crate-type=cdylib" "-Clink-arg=-Wl,--skip-wit-component"
status: exit status: 1
stderr:
error: linking with `/opt/hostedtoolcache/wasi-sdk-29.0-x86_64-linux/bin/clang` failed: exit status: 1
|
= note: "/opt/hostedtoolcache/wasi-sdk-29.0-x86_64-linux/bin/clang" "-Wl,--no-export-dynamic" "-Wl,--export" "-Wl,run" "-Wl,--export" "-Wl,cabi_realloc" "-Wl,-z" "-Wl,stack-size=1048576" "-Wl,--stack-first" "-Wl,--no-demangle" "<2 object files omitted>" "-ldylib_dep" "/lib/rustlib/wasm32-wasip2/lib/libpanic_abort-*.rlib" "/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/wasm32-wasip2/debug/libwit_bindgen.rlib" "/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/wasm32-wasip2/debug/deps/{libfutures-b27c7f5ef205c54f,libfutures_executor-922299a107bb047a,libfutures_util-9dc6196014b01a3f,libmemchr-42aea3167221f1c8,libfutures_io-8f5dbb637f9af8fd,libslab-e7bcb3e3d56d11ea,libfutures_channel-e0220edc4c5fb7be,libpin_project_lite-6a517c497ca1cc61,libfutures_sink-47a2cb5e9ef840c0,libfutures_task-df6ab379a1a807af,libfutures_core-f82a2f8330c0d626,libbitflags-860f6eb07a090227}.rlib" "/lib/rustlib/wasm32-wasip2/lib/{libstd-*,libwasip2-*,libwit_bindgen-*,libcfg_if-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,liblibc-*}.rlib" "-lc" "/lib/rustlib/wasm32-wasip2/lib/{librustc_std_workspace_core-*,liballoc-*,libcore-*,libcompiler_builtins-*}.rlib" "--target=wasm32-wasip2" "-L" "/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/rust/wit-bindgen/target/wasm32-wasip2/debug/build/wit-bindgen-41a5941b58e7a593/out" "-L" "/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/dylibs/runner-rust" "-o" "/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/dylibs/runner-rust.core.wasm" "-Wl,--gc-sections" "-static" "-shared" "-nodefaultlibs" "-shared" "-Wl,--skip-wit-component"
= note: some arguments are omitted. use `--verbose` to show all linker arguments
= note: wasm-ld: warning: creating shared libraries, with -shared, is not yet stable
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
error: failed to invoke LLD: signal: 11 (SIGSEGV) (core dumped)
clang: error: linker command failed with exit code 1 (use -v to see invocation)


error: aborting due to 1 previous error

failures:
tests/runtime/rust/dylibs/runner.rs

```

an example failure with wasi-sdk-32 is [here](https://github.com/bytecodealliance/wit-bindgen/actions/runs/33080429786/job/98546017557)

```
---- tests/runtime/variants/test.cs ----
component: test
path: tests/runtime/variants/test.cs
error: failed to compile component "tests/runtime/variants/test.cs"

Caused by:
command execution failed
command: cd "/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings" && "/usr/share/dotnet/dotnet" "publish" "/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/TestWorld.csproj" "-r" "wasi-wasm" "-c" "Debug" "/p:PlatformTarget=AnyCPU" "/p:MSBuildEnableWorkloadResolver=false" "--self-contained" "/p:UseAppHost=false" "-o" "/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/csharp-testcase"
status: exit status: 1
stdout:
Determining projects to restore...
Restored /home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/TestWorld.csproj (in 1.28 sec).
TestWorld -> /home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/bin/Debug/net10.0/wasi-wasm/csharp-testcase.dll
/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/.packages/microsoft.dotnet.ilcompiler.llvm/10.0.0-rc.1.26357.1/build/Microsoft.NETCore.Native.Wasm.targets(48,5): warning : Wasi SDK version 33.0+m is being used. This differs from the expected 29.0 and might result in build or runtime failures. [/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/TestWorld.csproj]
Generating native code
LLVM compilation to IR finished in 6.14 seconds
LLVM generation of bitcode finished in 0.62 seconds
LLVM generation of debug info finished in 0.11 seconds
Object writing finished in 0.64 seconds, allocated 36.63 MB
wasm-ld : error : --global-base cannot be less than stack size when --stack-first is used [/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/TestWorld.csproj]
EXEC : error : failed to invoke LLD: exit status: 1 [/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/TestWorld.csproj]
clang : error : linker command failed with exit code 1 (use -v to see invocation) [/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/TestWorld.csproj]
/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/.packages/microsoft.dotnet.ilcompiler.llvm/10.0.0-rc.1.26357.1/build/Microsoft.NETCore.Native.targets(616,5): error MSB3073: The command ""/opt/hostedtoolcache/wasi-sdk-33.0-x86_64-linux/bin/clang" @obj/Debug/net10.0/wasi-wasm/native/link.rsp " exited with code 1. [/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/TestWorld.csproj]
```

and example failure with wasi-sdk-34 is [here](https://github.com/bytecodealliance/wit-bindgen/actions/runs/33079380589/job/98542079915)

```
---- tests/runtime/variants/test.cs ----
component: test
path: tests/runtime/variants/test.cs
error: failed to compile component "tests/runtime/variants/test.cs"

Caused by:
command execution failed
command: cd "/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings" && "/usr/share/dotnet/dotnet" "publish" "/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/TestWorld.csproj" "-r" "wasi-wasm" "-c" "Debug" "/p:PlatformTarget=AnyCPU" "/p:MSBuildEnableWorkloadResolver=false" "--self-contained" "/p:UseAppHost=false" "-o" "/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/csharp-testcase"
status: exit status: 1
stdout:
Determining projects to restore...
Restored /home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/TestWorld.csproj (in 1.28 sec).
TestWorld -> /home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/bin/Debug/net10.0/wasi-wasm/csharp-testcase.dll
/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/.packages/microsoft.dotnet.ilcompiler.llvm/10.0.0-rc.1.26357.1/build/Microsoft.NETCore.Native.Wasm.targets(48,5): warning : Wasi SDK version 33.0+m is being used. This differs from the expected 29.0 and might result in build or runtime failures. [/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/TestWorld.csproj]
Generating native code
LLVM compilation to IR finished in 6.14 seconds
LLVM generation of bitcode finished in 0.62 seconds
LLVM generation of debug info finished in 0.11 seconds
Object writing finished in 0.64 seconds, allocated 36.63 MB
wasm-ld : error : --global-base cannot be less than stack size when --stack-first is used [/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/TestWorld.csproj]
EXEC : error : failed to invoke LLD: exit status: 1 [/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/TestWorld.csproj]
clang : error : linker command failed with exit code 1 (use -v to see invocation) [/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/TestWorld.csproj]
/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/.packages/microsoft.dotnet.ilcompiler.llvm/10.0.0-rc.1.26357.1/build/Microsoft.NETCore.Native.targets(616,5): error MSB3073: The command ""/opt/hostedtoolcache/wasi-sdk-33.0-x86_64-linux/bin/clang" @obj/Debug/net10.0/wasi-wasm/native/link.rsp " exited with code 1. [/home/runner/work/wit-bindgen/wit-bindgen/target/artifacts/variants/test-csharp/bindings/TestWorld.csproj]
```

cc @yowl

Start with the CI configuration and reproduce the failures in tests/runtime/rust/dylibs/runner.rs and tests/runtime/variants/test.cs using the referenced wasi-sdk versions. Compare the linker errors across SDK 29, 32, and 34, then verify that C# tests can be re-enabled and the affected runtime and variants tests complete successfully.

Written by the indexing model from the issue text.