fix(matcher): prevent CEL from matching label events unintentionally

[theakshaypant]

📝 Description of the Change

Add AST inspection in CEL evaluation to skip label events unless expression explicitly references labels. The AST walker checks "event_type" variable or ".labels" field This prevents generic "event == pull_request" CEL expressions unintentionally matching on label add/remove events.

👨🏻‍ Linked Jira

https://issues.redhat.com/browse/SRVKP-8491

🔗 Linked GitHub Issue

N/A

🚀 Type of Change

• [x] 🐛 Bug fix (fix:)
• [ ] ✨ New feature (feat:)
• [ ] 💥 Breaking change (feat!:, fix!:)
• [ ] 📚 Documentation update (docs:)
• [ ] ⚙️ Chore (chore:)
• [ ] 💅 Refactor (refactor:)
• [ ] 🔧 Enhancement (enhance:)
• [ ] 📦 Dependency update (deps:)

🧪 Testing Strategy

• [x] Unit tests
• [ ] Integration tests
• [ ] End-to-end tests
• [x] Manual testing
• [ ] Not Applicable

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✅ Submitter Checklist

• [x] 📝 My commit messages are clear, informative, and follow the project's How to write a git commit message guide. The Gitlint linter ensures in CI it's properly validated
• [x] ✨ I have ensured my commit message prefix (e.g., fix:, feat:) matches the "Type of Change" I selected above.
• [x] ♽ I have run make test and make lint locally to check for and fix any issues. For an efficient workflow, I have considered installing pre-commit and running pre-commit install to automate these checks.
• [ ] 📖 I have added or updated documentation for any user-facing changes.
• [x] 🧪 I have added sufficient unit tests for my code changes.
• [ ] 🎁 I have added end-to-end tests where feasible. See README for more details.
• [ ] 🔎 I have addressed any CI test flakiness or provided a clear reason to bypass it.
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