Add callable workflow for extension repositories (#43082)

This starts the work on a workflow that can be invoked in extension CI
to test changes on extension repositories.

Release Notes:

- N/A

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Co-authored-by: Agus Zubiaga <agus@zed.dev>
Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>
2a2f5a9c7aFinn Evers committed on 11/19/2025, 5:47:34 PM· committed by GitHubparent97b4299
15 files changedLine totals unavailable