Filter filelist for CI

[Erovia]

Description

The format workflow has limited scope, but will happily run on anything if even one of the touched files are from its scope.
This PR filters down the file list that is passed to qmk cformat to the paths that are actually in scope.

Test case:
#12597 fails because keyboard files are "incorrectly" formatted.
Erovia#1 fails because a core file is incorrectly formatted.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).