CI: Integrate workflow_triggers for xr-samples from cartland's fork

[cartland]

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

This is part of a batch of pull requests across repositories owned by the android organization on GitHub.
We are checking to make sure GitHub Actions are correctly using the following 3 triggers: workflow_dispatch, push, pull_request. This change modifies at least one of the following triggers:

1. workflow_dispatch: This trigger allows the workflow to be manually run in the GitHub UI. Most workflows should contain this trigger.
2. push: Most build and test scripts should run after a change is merged. This should at least run on the default branch, like main, but it could be configured to run on more branches.
3. pull_request: Most build and test scripts should run on pull requests, at least to the main branch.

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]

Note

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

[fuentespatrick]

LGTM