Tests

Respect gitignore #1121

Job	Run time
incremental-mutants	5m 32s
cargo-mutants	1h 17m 23s
build (macOS-latest, stable)	2m 10s
build (macOS-latest, nightly)	2m 34s
build (macOS-latest, 1.70)	3m 21s
build (ubuntu-latest, stable)	1m 22s
build (ubuntu-latest, nightly)	1m 21s
build (ubuntu-latest, 1.70)	1m 36s
build (windows-latest, stable)	2m 39s
build (windows-latest, nightly)	2m 16s
build (windows-latest, 1.70)	2m 19s
	1h 42m 33s

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