[llvm] [workflows] Delete user branches that are too long (PR #82845)

[Tom Stellard via llvm-commits]

tstellar wrote:

Is it possible for users to tell spr to create the branch, but not the PR?  If it's just a timing issue, we could have the workflow wait for a few minutes until it sees the PR.

https://github.com/llvm/llvm-project/pull/82845