ci: fix dependency pinning #1172

Job	Run time
examples-darwin	3m 33s
check-dead-code	30s
check-fmt	22s
examples-linux (alt-registry)	1m 3s
tests (https://releases.nixos.org/nix/nix-2.18.2/install)	3m 4s
examples-linux (build-std)	2m 11s
tests (https://releases.nixos.org/nix/nix-2.18.2/install, --override-input nixpkgs $(./ci/ref-fro...	4m 18s
examples-linux (cross-musl)	1m 31s
examples-linux (cross-rust-overlay)	1m 47s
examples-linux (cross-windows)	1m 25s
examples-linux (custom-toolchain)	1m 28s
examples-linux (end-to-end-testing)	3m 55s
examples-linux (quick-start)	1m 23s
examples-linux (quick-start-simple)	1m 4s
examples-linux (quick-start-workspace)	1m 33s
examples-linux (sqlx)	1m 3s
examples-linux (trunk-workspace)	3m 4s
examples-linux (trunk)	2m 1s
all systems go	0s
	35m 15s

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