bug(reload exclude dir): Resolve directory path before comparing to path.parents()

[schloerke]

Summary

This is just the bug fix from #2602

• bug: Checking if a excluded path is within a path's .parents() only works if the excluded path is an absolute path.
  • The watched paths (config.reload_dirs) are absolute, so the path parents are also absolute.
  • Therefore, all excluded dirs in FileFilter should also be absolute paths.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• [NA] I've updated the documentation accordingly.