[llvm] Changed Regex to accept /branch: and /cherry-pick: commands (PR #81002)

[Tom Stellard via llvm-commits]

tstellar wrote:

> This is a rather trivial issue. If this is not relevant anymore, I will close the PR and you can mark the issue as resolved. Though I do think that adding regex support for cherry-pick seems prudent.

I think this is fine, but maybe remove the comment about the obsolete /branch command in another patch.

https://github.com/llvm/llvm-project/pull/81002