Auto merge of #121992 - jieyouxu:fix-tidy-unpaired-revision, r=onur-ozkan

tidy: split dots in filename not the entire path when checking for stray stdout/stderr files

I committed a path crime by splitting the entire path on `.`, when I meant to split on the filename. This means that any parent folders which contain `.` will cause tidy failure. Added a regression test so that doesn't happen again.

### Follow-up

- [ ] Adjust rustc-dev-guide to document assert on test name not containing dots. rust-lang/rustc-dev-guide#1927

Fixes #121986.

Author: bors