fix-clang-format target erases content of files from .clang-format-ignore

[HendrikTi]

Using the fix-clang-format with a .clang-format-ignore file results in erased file contents for all files matched by the .clang-format-ignore file.

This was resolved with llvm/llvm-project#102629, where -list-ignored was added to clang-format to let git-clang-format handle ignored files. Therefore updating the git-clang-format.py would be required to fix this.