Update shared personal token to use a generated primer app token

[jonrohan]

https://github.com/github/primer/issues/6097

What are you trying to accomplish?

This pull request updates the static files workflow to improve authentication and token management for GitHub Actions. The main change is switching to a GitHub App token for secure operations, replacing the previous use of a shared personal access token.

Risk Assessment

• Low risk the change is small, highly observable, and easily rolled back.
• Medium risk changes that are isolated, reduced in scope or could impact few users. The change will not impact library availability.
• High risk changes are those that could impact customers and SLOs, low or no test coverage, low observability, or slow to rollback.

Anything you want to highlight for special attention from reviewers?

I think I also want to change this to always run. We had restricted it to main because the commit on a branch would block ci, but with the app that doesn't happen.

[changeset-bot]

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Latest commit: af4eb56

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[Copilot]

Pull request overview

This pull request modernizes the static files workflow by transitioning from a shared personal access token to a GitHub App token for authentication. This change improves security and allows the workflow to run on all pushes (not just the main branch) since GitHub App tokens don't trigger additional CI workflows like personal access tokens do.

Key changes:

• Replaced static personal access token (GPR_AUTH_TOKEN_SHARED) with dynamically generated GitHub App token
• Removed branch restriction to enable workflow execution on all pushes
• Removed outdated comment about branch protection limitations with GitHub Apps

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[llastflowers]

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