Slightly more `std::filesystem` for `nix eval` #1670

Job	Run time
Check Cachix and Docker secrets present for installer tests	1s
vm_tests	12m 54s
tests (ubuntu-latest)	21m 50s
tests (macos-latest)	46m 37s
flake_regressions	0s
installer	0s
docker_push_image	0s
installer_test	0s
	1h 21m 22s

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