Fix deeply nested registries (#676) #1167

Job	Run time
check-fmt	23s
examples-darwin	8m 53s
examples-linux (alt-registry)	2m 42s
tests (https://releases.nixos.org/nix/nix-2.18.2/install)	12m 46s
examples-linux (build-std)	2m 6s
tests (https://releases.nixos.org/nix/nix-2.18.2/install, --override-input nixpkgs $(./ci/ref-fro...	14m 1s
examples-linux (cross-musl)	1m 5s
examples-linux (cross-rust-overlay)	1m 37s
check-dead-code	25s
examples-linux (cross-windows)	1m 26s
examples-linux (custom-toolchain)	1m 2s
examples-linux (end-to-end-testing)	3m 46s
examples-linux (quick-start)	1m 9s
examples-linux (quick-start-simple)	1m 3s
examples-linux (quick-start-workspace)	2m 20s
examples-linux (sqlx)	4m 0s
examples-linux (trunk-workspace)	3m 34s
examples-linux (trunk)	2m 25s
all systems go	0s
	1h 4m 43s

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