[llvm] [workflows] Close issues used for backports once the PR has been created (PR #80394)

[Tom Stellard via llvm-commits]

tstellar wrote:

> Hm, before we have had the issue open until we had merged the PR. In case some of the needs some further discussion and revisions. Should we just do those comments and revisions directly in the PR going forward?

Yes, I was thinking we should try to push all the discussions to the PR, because that is where all the other activity is happening for the most part (e.g. patch gets reviewed, patch gets tested, patch gets merged)

The alternative would be to add a new status to the LLVM release status project called "PR Created".  In this case,  we would leave the issue open and assign it this new "PR Created" status.  Then the other statuses would be tracked only on the PR: e.g."Needs Review", "Needs Merged".

https://github.com/llvm/llvm-project/pull/80394