Suppress warnings emitted by Checker Framework version 3.0.0

More information:
https://docs.google.com/document/d/16tpK6aXqN68PvTyvt4siM-m7f0NXi_8xEeitLDzr8xY/edit?usp=sharing
Tested:
    TAP --sample ran all affected tests and none failed
    http://test/OCL:279845168:BASE:279870402:1573537714395:80ca701c
PiperOrigin-RevId: 279891832

library/ui/src/main/java/com/google/android/exoplayer2/ui/PlayerNotificationManager.java

@@ -1006,6 +1006,8 @@ public class PlayerNotificationManager {
    *     NotificationCompat.Builder#build()} to obtain the notification, or {@code null} if no
    *     notification should be displayed.
    */
+  // incompatible types in argument.
+  @SuppressWarnings("nullness:argument.type.incompatible")
   @Nullable
   protected NotificationCompat.Builder createNotification(
       Player player,