meta.tests: rename into passthru.tests

Nix currently rejects derivations in `meta` values. This works around
that limitation by using `passthru` instead.

Closes https://github.com/NixOS/nixpkgs/issues/50230

pkgs/stdenv/generic/check-meta.nix

@@ -166,6 +166,7 @@ let
     hydraPlatforms = listOf str;
     broken = bool;
     # TODO: refactor once something like Profpatsch's types-simple will land
+    # This is currently dead code due to https://github.com/NixOS/nix/issues/2532
     tests = attrsOf (mkOptionType {
       name = "test";
       check = x: x == {} || ( # Accept {} for tests that are unsupported