Add method signature

Author: jugglinmike

tools/ci/update_pr_preview.py

@@ -104,6 +104,9 @@ def get_revision(self, refspec):
 
         return output.split()[0]
 
+    def update_ref(self, refspec, revision):
+        raise NotImplementedError()
+
     def delete_ref(self, refspec):
         with self._make_temp_repo() as temp_repo:
             subprocess.check_call(