Tests

WIP: Read diffs so we can filter by them #1090

Job	Run time
build (macOS-latest, stable)	2m 41s
build (macOS-latest, nightly)	2m 27s
build (macOS-latest, 1.70)	2m 57s
build (ubuntu-latest, stable)	3m 4s
build (ubuntu-latest, nightly)	1m 29s
build (ubuntu-latest, 1.70)	2m 56s
build (windows-latest, stable)	4m 21s
build (windows-latest, nightly)	3m 14s
build (windows-latest, 1.70)	5m 36s
cargo-mutants	2h 33m 51s
	3h 2m 36s

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