Add workflows write permission for workflow PRs

[sentry-junior]

PRs that touch .github/workflows/ files fail because the GitHub App token lacks the workflows write permission. This blocks Junior from making PRs that add or update CI workflows.

• GitHub requires explicit workflows write scope to push commits that modify workflow files
• Current token permissions don't include this scope
• Affects any PR that needs to add, update, or remove workflow YAML

Considerations:

• The workflows permission is sensitive — it grants ability to modify CI/CD pipelines
• Scope the permission to repos where Junior actively operates, if possible
• Verify whether the GitHub App manifest or installation-level settings need updating

Action taken on behalf of David Cramer.