Coverage on CI builds manual targets

Apparently, our coverage CI targets build the [manual targets](https://github.com/bazelbuild/rules_rust/pull/2480/files#diff-2f6b2cb6597a89a9ccb014fdeb44c941bfb3587cdc3481afdb5a65525df434c7R33) which are only intended for analysis tests. See https://buildkite.com/bazel/rules-rust-rustlang/builds/10609#018db017-013b-47b3-8ff0-13d7ee74d774 for the error

```
(05:20:02) ERROR: /Users/buildkite/builds/bk-imacpro-15/bazel/rules-rust-rustlang/test/bindgen/BUILD.bazel:3:19: Compiling Rust bin test_cc_linkopt_rust_binary (1 files) failed: missing input file '//test/bindgen:main.rs'
--
  | (05:20:02) ERROR: /Users/buildkite/builds/bk-imacpro-15/bazel/rules-rust-rustlang/test/bindgen/BUILD.bazel:3:19: Compiling Rust bin test_cc_linkopt_rust_binary (1 files) failed: 1 input file(s) do not exist
  | (05:20:02) ERROR: /Users/buildkite/builds/bk-imacpro-15/bazel/rules-rust-rustlang/test/bindgen/BUILD.bazel:3:19 Compiling Rust bin test_cc_linkopt_rust_binary (1 files) failed: 1 input file(s) do not exist
```

Apparently, our `test/` folder has a mixed bag of both analysis tests and examples. Analysis tests should mostly include manual targets which shouldn't require any inputs at all. A holistic fix should be drawing the clear borderline so that `bazel coverage` doesn't run against the `manual` targets. @UebelAndre I remember you talking about this at some point. Do you have suggestion what we should do here?

cc: @scentini