Add triggers to .github/workflows/

[cartland]

This PR standardizes GitHub Actions triggers in workflow files within .github/workflows/.

The goal is to ensure workflows run consistently on push, pull_request, and workflow_dispatch events where appropriate.

This is part of a batch of pull requests across repositories owned by the android organization on GitHub.

Project Owner: Please review the changes carefully to ensure they are correct and appropriate for this project before approving and merging.

• If you do not think this change is appropriate (e.g., a workflow should NOT run on one of these triggers), please leave a comment explaining why.
• If you think the goal is appropriate but notice a mistake in the implementation, please leave a comment detailing the mistake.

[gemini-code-assist[bot]]

[!WARNING] Gemini encountered an error creating the summary. You can try again by commenting /gemini summary.

[cartland]

One of the checks has been stuck since April 17 on "build / build Expected — Waiting for status to be reported". I just changed the commit message to see if I could poke GitHub to run the check again.

We cannot merge the pull request until the "1 pending check" has been completed.

[bentrengrove]

All good, I fixed it