fix: add group name to branch name

[bahrmichael]

Heya 👋

I'm intentionally opening this PR before being done with all the tests/docs because I'd like your feedback on this approach.

• Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea: Head branch does not contain group name #1923
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed) TBD
• Appropriate docs were updated (if necessary) TBD

Fixes #1923 🦕

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[bahrmichael]

I change this file to add and run the Merge plugin afterwards, because that way the if condition was much simpler to read.

I'm expanding the if condition to also check for the number of new pull requests, so that it won't attempt a merge if there aren't multiple PRs that should be merged together. While updating the code for the linked-versions project we encountered a problem where one remaining PR was renamed because of the merge attempt of 1 PR.

[bahrmichael]

@chingor13 Could you take a look at this?