Merge pull request #178 from cachix/refactor #385

Job	Run time
installCommand (ubuntu-latest)	36s
installCommand (macos-latest)	1m 37s
private-cache (ubuntu-latest, true)	40s
public-cache-no-signing-key (ubuntu-latest, true)	34s
private-cache (ubuntu-latest, false)	38s
public-cache (ubuntu-latest, true)	38s
public-cache-no-signing-key (ubuntu-latest, false)	31s
private-cache (macos-latest, true)	1m 35s
public-cache (ubuntu-latest, false)	41s
public-cache-no-signing-key (macos-latest, true)	1m 27s
private-cache (macos-latest, false)	1m 30s
nix-master (ubuntu-latest)	40s
public-cache (macos-latest, true)	1m 39s
public-cache-no-signing-key (macos-latest, false)	1m 54s
nix-master (macos-latest)	1m 28s
public-cache (macos-latest, false)	1m 43s
	17m 51s

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