Bug 1691166 - Replace deprecated enum constant NSSystemDefined with NSEventTypeSystemDefined in TestMediaKeysEventMac.mm. r=spohl

Differential Revision: https://phabricator.services.mozilla.com/D104298

Author: mstange

dom/media/mediacontrol/tests/gtest/TestMediaKeysEventMac.mm

@@ -19,7 +19,7 @@
 static const int kSystemDefinedEventMediaKeysSubtype = 8;
 
 static void SendFakeEvent(RefPtr<MediaHardwareKeysEventSourceMac>& aSource, int aKeyData) {
-  NSEvent* event = [NSEvent otherEventWithType:NSSystemDefined
+  NSEvent* event = [NSEvent otherEventWithType:NSEventTypeSystemDefined
                                       location:NSZeroPoint
                                  modifierFlags:0
                                      timestamp:0