ci: trigger AI rebase agent from autoroll_chromium when conflicted PR created

[linxinan-yt]

Configures .github/workflows/autoroll_chromium.yaml to automatically dispatch the ai_rebase_resolver.yaml workflow whenever a newly created Chromium autoroll PR contains merge or cherry-pick conflicts (CONFLICTED).

Bug: 552561778

[gemini-code-assist]

Note

Gemini is unable to generate a review for this pull request due to the file types involved not being currently supported.

[github-actions]

🤖 Gemini Suggested Commit Message

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ci: Trigger AI rebase for conflicted autorolls

Configure the Chromium autoroll workflow to automatically invoke the AI
rebase resolver whenever a generated pull request contains merge or
cherry-pick conflicts. This integration accelerates the roll process
by attempting automated conflict resolution immediately upon detection,
reducing the manual workload required to maintain the Chromium fork.

The workflow now manages the necessary permissions and state to track
conflicted pull requests and dispatch the subsequent resolution logic.

Bug: 552561778

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[oxve]

I think you need the actions: write permission for this call. Add it above to the autoroll job permissions list.