chore(CI): split PR labeler workflow

[chenjiahan]

Summary

Separate the PR Labeler workflow, because:

• It is not appropriate to put it below the Lint PR Title workflow.
• It requires pull-requests: write permission, separating it allows for isolation of permissions.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[netlify]

✅ Deploy Preview for rspack canceled.

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[codspeed-hq]

CodSpeed Performance Report

Merging #9102 will not alter performance

_{Comparing pr_labeler_workflow_0123 (d58026f) with main (494aaa1)}

Summary

✅ 4 untouched benchmarks