Log a warning if the RTDB connection is forcefully killed. (#2787)

* Log a warning if the RTDB connection is forcefully killed.

* Fmt

Author: jsdt

firebase-database/src/main/java/com/google/firebase/database/connection/PersistentConnectionImpl.java

@@ -559,10 +559,11 @@ public void onDisconnect(Connection.DisconnectReason reason) {
 
   @Override
   public void onKill(String reason) {
-    if (logger.logsDebug())
-      logger.debug(
-          "Firebase Database connection was forcefully killed by the server. Will not attempt reconnect. Reason: "
-              + reason);
+    logger.warn(
+        "Firebase Database connection was forcefully killed by the server. Will not attempt"
+            + " reconnect. Reason: "
+            + reason);
+
     interrupt(SERVER_KILL_INTERRUPT_REASON);
   }