CMake integration: CTest test list does not work when cross-compiling without CROSSCOMPILING_EMULATOR

**Describe the bug**
If I run `ctest --show-only` inside the build dir of a cross-compiled project that uses `catch_discover_tests`, it doesn't print any tests but the failed `execute_process` does not fail the build (it just prints `cannot execute binary file` and continues because the output is not equal to `0`.

I can see that the documentation states:
> it requires that :prop_tgt:`CROSSCOMPILING_EMULATOR` is properly set in order to function in a cross-compiling environment.

However, I think it would be good if `CatchAddTests.cmake` could just add a single `add_test()` that invokes the Catch2 binary without any filtering if the listing fails.

**Reproduction steps**

Cross-compile any project that uses the Catch2 CMake integration without CMAKE_CROSS_COMPILING_EMULATOR and then run ctest --show-only in the build directory.

**Platform information:**

- Catch version: **v2.13.6**
- Cross-compiling for FreeBSD from macOS.

**Additional context**
In order to build and run tests I don't (can't) use CMAKE_CROSS_COMPILING_EMULATOR. Instead I build the tests, start a QEMU VM, mount the build directory via SMBFS and run them manually (well I have a [set of python scripts that do all of this](https://github.com/CTSRD-CHERI/cheribuild/pull/192/files)).
Ideally I'd like ctest to drive that process rather than having to hardcode the list of tests.