Revert "nix: 2.18 -> 2.22"

[fricklerhandwerk]

Reverts #315262 cc @Mic92 @lovesegfault

Looking into fixing the test failure https://hydra.nixos.org/build/261759976/nixlog/18 here

nixpkgs/nixos/tests/misc.nix

Lines 75 to 86 in d8a5a62

	with subtest("nix-db"):
	info = get_path_info("${foo}")
	print(info)
	if (
	info[0]["narHash"]
	!= "sha256-BdMdnb/0eWy3EddjE83rdgzWWpQjfWPAj3zDIFMD3Ck="
	):
	raise Exception("narHash not set")
	if info[0]["narSize"] != 128:
	raise Exception("narSize not set")