[Repo] Skip label workflow on forks

[martincostello]

Changes

Skip labelling on forks.

I accidentally opened a PR in my fork, then noticed that the labelling job failed because my fork doesn't contain this repo's labels.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[Copilot]

Pull request overview

This PR adds fork detection to the label workflow to prevent failures when pull requests or issues are opened in forked repositories that don't have the same label configuration as the upstream repository.

• Added github.event.repository.fork == false condition to both labeling jobs
• Prevents workflow failures in forks due to missing labels

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.69%. Comparing base (c6a203f) to head (b83626e).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6765      +/-   ##
==========================================
- Coverage   86.73%   86.69%   -0.05%     
==========================================
  Files         262      262              
  Lines       12319    12319              
==========================================
- Hits        10685    10680       -5     
- Misses       1634     1639       +5     

Flag	Coverage Δ
unittests-Project-Experimental	86.38% <ø> (-0.30%)	⬇️
unittests-Project-Stable	86.66% <ø> (ø)
unittests-Solution	86.58% <ø> (-0.20%)	⬇️
unittests-UnstableCoreLibraries-Experimental	86.07% <ø> (ø)

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see 2 files with indirect coverage changes