Enhance Configure git CLI for an app's bot user action example

[CannonLock]

Enhances the current example with a checkout step for completeness and to demonstrate the important step of not persisting the credentials.

Other users have ran into this issue: #75

[Copilot]

Pull Request Overview

This PR enhances the "Configure git CLI for an app's bot user" example in the README by adding a crucial checkout step that demonstrates proper credential handling. The change addresses a common issue where users weren't aware of the need to prevent persisting default GITHUB_TOKEN credentials when using app tokens.

• Adds a checkout step with persist-credentials: false to prevent credential conflicts
• Includes explanatory comment about preventing implicit use of default GITHUB_TOKEN

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[gr2m]

Alternatively, you can use the token from the app to checkout the code

 - uses: actions/create-github-app-token@v2 id: app-token with: # required app-id: ${{ vars.APP_ID }} private-key: ${{ secrets.PRIVATE_KEY }} - name: Checkout code uses: actions/checkout@v4 with: token: ${{ steps.app-token.outputs.token }} 

Not sure which one is better. I think persist-credentials: false is a best practice either way when it's not needed for subsequent pulls or pushes.

[CannonLock]

Closing in favor of #288 which provides a example closer to what I was looking for in the README.