Install stack if necessary #277

Job	Run time
test-fails-on-error	14s
test-generate	3s
test (ubuntu-latest, nightly)	32s
test (ubuntu-latest, lts)	40s
test (ubuntu-latest, lts-22.7, 9.6.4)	24s
test (ubuntu-latest, lts-12.26, 8.4.4)	32s
test (macOS-latest, nightly)	37s
test (macOS-latest, lts)	52s
test (macOS-latest, lts-22.7, 9.6.4)	35s
test (windows-latest, nightly)	3m 22s
test (windows-latest, lts)	3m 22s
test (windows-latest, lts-22.7, 9.6.4)	2m 41s
test (windows-latest, lts-12.26, 8.4.4)	2m 28s
test-stack-yamls (stack-nightly.yaml)	40s
test-stack-yamls (stack.yaml)	22s
	17m 24s

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