[chore](regression) Enable branch-4.2 pull request CI routing

[hello-stephen]

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #67744

Problem Summary: Pull requests targeting branch-4.2 are not mapped to the community TeamCity pipelines, and Vault P0 rejects branch-4.2 during preparation. Add a branch-4.2-specific matrix aligned with branch-4.1, excluding Performance and ARM, and allow Vault P0 preparation for branch-4.2. Existing mappings in the branch-4.2 baseline remain unchanged.

Release note

None

Check List (For Author)

• Test: Manual test
  • Validated shell syntax and the exact branch-4.2 pipeline mapping.
• Behavior changed: Yes (pull requests targeting branch-4.2 are routed to the supported community CI matrix)
• Does this need documentation: No

[hello-stephen]

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