test,mmrules: fix warnings with -Wswitch-default

mmrules.c: In function ‘print_rule’:
  mmrules.c:97:13: error: switch missing default case [-Werror=switch-default]
     97 |             switch (rule_match->type) {
        |             ^~~~~~
  mmrules.c:113:5: error: switch missing default case [-Werror=switch-default]
    113 |     switch (rule->result.type) {
        |     ^~~~~~

test/mmrules.c

@@ -104,6 +104,7 @@ print_rule (MMUdevRule *rule)
                          i, rule_match->parameter, rule_match->value);
                 break;
             case MM_UDEV_RULE_MATCH_TYPE_UNKNOWN:
+            default:
                 g_assert_not_reached ();
             }
         }
@@ -123,6 +124,7 @@ print_rule (MMUdevRule *rule)
         break;
     case MM_UDEV_RULE_RESULT_TYPE_GOTO_TAG:
     case MM_UDEV_RULE_RESULT_TYPE_UNKNOWN:
+    default:
         g_assert_not_reached ();
     }
 }