`om ci`: Copy results back from remote Nix store #1398

Job	Run time
main (x86_64-linux, false)	3m 39s
main (aarch64-darwin, false)	6m 9s
static-binary-check (ubuntu-latest)	2s
website	0s
static-binary-check (macos-latest)	5s
	9m 55s

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