Set up infrastructure for lockstep-style testing #90

Job	Run time
cabal-fmt (9.2.8, 3.10.1.0, ubuntu-latest)	2m 19s
stylish-haskell (9.2.8, 3.10.1.0, ubuntu-latest)	2m 33s
cabal-check (9.6.2, 3.10.1.0, ubuntu-latest)	30s
build (8.10.7, 3.10.1.0, ubuntu-latest)	2m 8s
build (8.10.7, 3.10.1.0, windows-latest)	4m 9s
build (8.10.7, 3.10.1.0, macOS-latest)	5m 35s
build (9.2.8, 3.10.1.0, ubuntu-latest)	2m 33s
build (9.2.8, 3.10.1.0, windows-latest)	8m 16s
build (9.2.8, 3.10.1.0, macOS-latest)	1m 58s
build (9.4.6, 3.10.1.0, ubuntu-latest)	3m 14s
build (9.4.6, 3.10.1.0, windows-latest)	6m 27s
build (9.4.6, 3.10.1.0, macOS-latest)	6m 35s
build (9.6.2, 3.10.1.0, ubuntu-latest)	1m 7s
build (9.6.2, 3.10.1.0, windows-latest)	4m 2s
build (9.6.2, 3.10.1.0, macOS-latest)	1m 23s
	52m 49s

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