utils/github: support multiple commits in create_bump_pr

[cho-m]

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Initial draft to add support for multiple commits, which can be used to support synced formulae bumps (#16383)

[cho-m]

May switch to a Struct to be more explicit rather than having to read docs to know what index means.

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.