Closes #5380: Add steps to pull requests created by Prepare for minor release workflow

[bberndt-uaz]

Description

This PR makes these changes to the Prepare repository for new minor release workflow:

• For the auto-generated PR targeting the release branch: Adds a step to update SCAFFOLD_BRANCH in the Tugboat config.
• For both auto-generated PRs: Adds a step to update the branches in the CI workflow YAML. Currently, this PR simply adds the release branch right after the 2.x branch.
• For both auto-generated PRs: Adds a custom description for the PRs noting that the CI workflow YAML needs review.

Once this PR is merged, I'll update the wiki page on creating minor releases.

Related issues

• Add steps to pull requests created by Prepare for minor release workflow #5380

How to test

Types of changes

Arizona Quickstart (install profile, custom modules, custom theme)

• Patch release changes
  • Bug fix
  • Accessibility, performance, or security improvement
  • Critical institutional link or brand change
  • Adding experimental module
  • Update experimental module
• Minor release changes
  • New feature
  • Breaking or visual change to existing behavior
  • Upgrade experimental module to stable
  • Enable existing module by default or database update
  • Non-critical brand change
  • New internal API or API improvement with backwards compatibility
  • Risky or disruptive cleanup to comply with coding standards
  • High-risk or disruptive change (requires upgrade path, risks regression, etc.)
• Other or unknown
  • Other or unknown

Drupal core

• Patch release changes
  • Security update
  • Patch level release (non-security bug-fix release)
  • Patch removal that's no longer necessary
• Minor release changes
  • Major or minor level update
• Other or unknown
  • Other or unknown

Drupal contrib projects

• Patch release changes
  • Security update
  • Patch or minor level update
  • Add new module
  • Patch removal that's no longer necessary
• Minor release changes
  • Major level update
• Other or unknown
  • Other or unknown

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My change requires release notes.

[joeparsons]

Really like this. Thanks!