fix: Check current default branch before modifying

[stevehipwell]

Resolves #2829

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Before the change?

• No check if github_branch_default needs to make changes

After the change?

• Check if github_branch_default requires changes

Pull request checklist

• Schema migrations have been created if needed (example)
• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes
• No

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