Correctly set clang_tidy_test exec groups

[keith]

If your execution and target platform differ, we have to make sure that
clang tidy, and the C++ toolchain, are configured for where the test
will execute, instead of where the test script is generated.

[erenon]

Thanks! CI seems to be failing.

[keith]

i'll leave off "@bazel_tools//tools/test:default_test_toolchain_type", for now, but that means with bazel 9.x+ that this could run on a different execution platform than the target platform (which was actually my goal here) even if you don't care about that case. probably fine since I imagine most folks won't care or have that setup, but something to note in case it comes up

[erenon]

thanks!