Turn default.nix into a function #151

Job	Run time
Build (8.10.7, 3.8, ubuntu-20.04)	2m 56s
Build (8.10.7, 3.8, ubuntu-22.04)	3m 2s
Build (8.10.7, 3.8, macOS-latest)	5m 11s
Build (9.0.2, 3.8, ubuntu-20.04)	2m 45s
Build (9.0.2, 3.8, ubuntu-22.04)	3m 3s
Build (9.0.2, 3.8, macOS-latest)	8m 56s
Build (9.2, 3.8, ubuntu-20.04)	1m 28s
Build (9.2, 3.8, ubuntu-22.04)	1m 40s
Build (9.2, 3.8, macOS-latest)	2m 15s
Build (9.4, 3.8, ubuntu-20.04)	1m 40s
Build (9.4, 3.8, ubuntu-22.04)	2m 15s
Build (9.4, 3.8, macOS-latest)	5m 12s
Build and publish docker image	0s
	40m 23s

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