[llvm] [MISched] Use right boundary when trying latency heuristics (PR #116592)

[Michael Maitland via llvm-commits]

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

LGTM. This is what GenericScheduler does in `tryCandidate` for `tryLatency`, so I think it makes sense to take it too.

https://github.com/llvm/llvm-project/pull/116592