postgresql: enable tests on darwin

they were disabled in 0c3b7ea but seems
to be working now

pkgs/servers/sql/postgresql/generic.nix

@@ -194,7 +194,7 @@ let
         wrapProgram $out/bin/initdb --prefix PATH ":" ${glibc.bin}/bin
       '';
 
-    doCheck = !stdenv'.isDarwin;
+    doCheck = true;
     # autodetection doesn't seem to able to find this, but it's there.
     checkTarget = "check";