[libc++][modules] Increase clang-tidy version used.

As suggested in #71438 we should use
  export import std;
in the std.compat module.

Testing this locally failed when building with the clang-tidy-17
plugin. The std module was considered corrupt in the test
  libcxx/test/libcxx/module_std_compat.gen.py
however the test
  libcxx/test/libcxx/module_std.gen.py
passed. Both test generated identical std.pcm files. Using the
clang-tidy-18 plugin solves the issue.