Rollup merge of #136291 - lcnr:compare-mode, r=oli-obk

some test suite cleanups

found while checking `compare-mode next-solver`

r? `@oli-obk`

<sub> [lcnr](https://github.com/rust-lang/rust/commits?author=lcnr) authored and JJ_EMPTY_STRING committed </sub>

Author: jhpratt