[llvm] [CI] Update setup-python action to v5 for GHA (PR #95414)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 approved this pull request.

LGTM.

I'm assuming you just grepped for all v4 action uses in the repo (just want to confirm that we don't have any more lying around).

WWe should probably hash pin these at some point, but given they weren't before, probably something to do in a later patch.

Thanks!

https://github.com/llvm/llvm-project/pull/95414