Fix mysql test evaluation

nixos/tests/mysql.nix

@@ -9,6 +9,7 @@
         services.mysql.enable = true;
 	services.mysql.replication.role = "master";
 	services.mysql.initialDatabases = [ { name = "testdb"; schema = ./testdb.sql; } ];
+        services.mysql.package = pkgs.mysql;
       };
   };