Rollup merge of #137670 - RalfJung:llvm-commit-logic-revert, r=Kobzol

revert accidental change in get_closest_merge_commit

This was accidentally merged as part of rust-lang/rust#137594. I need this local diff to be able to debug miri syncs, and then typed `git commit -a` too fast and didn't realize it includes this change... sorry for that.

r? ``@Kobzol``