tests: remove type passthrough

Nix can only build attrsets with a `type = "derivation"` attr.

Having the configuration's option-type as a passthru attr breaks the
ability to build specific test entries, since they are no longer
`type = "derivation"`.

Author: MattSturgeon

tests/main.nix

@@ -37,9 +37,13 @@ let
     configuration.config.build.test.overrideAttrs (old: {
       passthru =
         old.passthru or { }
-        // builtins.removeAttrs configuration [ "_type" ]
+        // builtins.removeAttrs configuration [
+          "_type"
+          "type"
+        ]
         // {
           inherit file module;
+          optionType = configuration.type;
         };
     });