ci: cache Nix store with cache-nix-action #2167

Job	Run time
Build aarch64 (Cabal, GHC ${{ matrix.ghc }})	0s
Build Linux (Cabal, GHC 9.0.2)	24m 2s
Build MacOS (Nix)	9m 17s
Build Linux (Cabal, GHC 9.2.4)	20m 17s
Build Linux (Stack)	3m 38s
Build Linux static (Nix)	3m 16s
Build MacOS (Stack)	25m 42s
Get FreeBSD build from CirrusCI	15s
Build Windows (Stack)	36m 43s
Lint & check code style	2m 30s
Test memory (Nix)	4m 41s
Test (Nix)	8m 53s
Test PG 9.6 (Nix)	7m 13s
Test PG 10 (Nix)	7m 23s
Test PG 11 (Nix)	9m 14s
Test PG 12 (Nix)	8m 18s
Test PG 13 (Nix)	9m 17s
Test PG 14 (Nix)	7m 13s
Test PG 15 (Nix)	7m 41s
Test PG 16 (Nix)	7m 49s
Prepare release	0s
Release on Docker Hub	0s
Release on GitHub	0s
Release Arm Builds on Docker Hub	0s
Remove copied files from server	0s
	3h 23m 22s

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