Fix wrong call to unlock requests in merger client

Change-Id: Ic519132f211dc3613023e2bc2bd8f11b29c9ac42

zuul/merger/client.py

@@ -163,7 +163,7 @@ class MergeClient(object):
                     try:
                         self.merger_api.remove(request)
                     finally:
-                        self.executor_api.unlock(request)
+                        self.merger_api.unlock(request)
         finally:
             # Regardless of that, remove the waiter node
             job.cancel()