Tests

Mutate == to != and vice versa #1126

Job	Run time
cargo-mutants	2m 7s
incremental-mutants	2m 59s
build (macOS-latest, stable)	1m 35s
build (macOS-latest, nightly)	1m 35s
build (macOS-latest, 1.70)	1m 40s
build (ubuntu-latest, stable)	1m 28s
build (ubuntu-latest, nightly)	1m 21s
build (ubuntu-latest, 1.70)	1m 35s
build (windows-latest, stable)	1m 20s
build (windows-latest, nightly)	1m 26s
build (windows-latest, 1.70)	1m 31s
	18m 37s

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