Use same monitor for progress synchronization

Lock on the object we are about to update.

Change-Id: I45ce98ba16c018fd12febe5dd2d9ed00aabdd90a

gerrit-server/src/main/java/com/google/gerrit/server/git/ReceiveCommits.java

@@ -1663,7 +1663,7 @@ public class ReceiveCommits {
               }
             }
           } finally {
-            synchronized (newProgress) {
+            synchronized (replaceProgress) {
               replaceProgress.update(1);
             }
           }