checks: move all tests to the test flake #1366

Job	Run time
lints	58s
examples-darwin	2m 14s
tests (https://nixos.org/nix/install)	54s
examples-linux (alt-registry)	1m 31s
tests (https://releases.nixos.org/nix/nix-2.24.10/install, --override-input nixpkgs $(./ci/ref-fr...	1m 16s
examples-linux (build-std)	2m 4s
examples-linux (cross-musl)	1m 38s
examples-linux (cross-rust-overlay)	1m 37s
examples-linux (cross-windows)	1m 30s
examples-linux (custom-toolchain)	1m 31s
examples-linux (end-to-end-testing)	1m 39s
examples-linux (quick-start)	1m 31s
examples-linux (quick-start-simple)	1m 36s
examples-linux (quick-start-workspace)	1m 32s
examples-linux (sqlx)	1m 35s
examples-linux (trunk-workspace)	1m 34s
examples-linux (trunk)	1m 33s
all systems go	1s
	26m 14s

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