[infra] Fix a couple paths in PR auto-label file change detection

[CodeBlanch]

Changes

• Switch to / for all paths in PR auto-label script

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)

[CodeBlanch]

Noticed #5746 didn't automatically get assigned the perf label.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.20%. Comparing base (6250307) to head (063eabc).
Report is 280 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5751      +/-   ##
==========================================
+ Coverage   83.38%   86.20%   +2.82%     
==========================================
  Files         297      254      -43     
  Lines       12531    11057    -1474     
==========================================
- Hits        10449     9532     -917     
+ Misses       2082     1525     -557     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	86.12% <ø> (?)
unittests-Project-Stable	86.11% <ø> (?)
unittests-Solution	86.20% <ø> (?)
unittests-UnstableCoreLibraries-Experimental	85.86% <ø> (?)

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see 197 files with indirect coverage changes