code_formatter CI job double-escapes some filenames

It looks like the stage `git diff -U0 --pickaxe-regex` of the code_formatter CI job is making double-escapes, which breaks it on some filenames.

For example, it escapes `libcxx/test/std/strings/basic.string/string.nonmembers/string_op!=/pointer_string.pass.cpp` as `'libcxx/test/std/strings/basic.string/string.nonmembers/string_op\!=/pointer_string.pass.cpp'` - with both quotes and backslash, like here: https://github.com/llvm/llvm-project/actions/runs/24154735536/job/70509323338?pr=191023#step:5:8

This is likely not a problem, though, if the PR was formatted correctly.

Inspect the `code_formatter` CI job and its `git diff -U0 --pickaxe-regex` stage, then reproduce the behavior with the example filename from the issue. Done means filenames are not double-escaped while correctly formatted pull requests continue to pass the job.

Written by the indexing model from the issue text.