Try pulling twice instead of thrice before giving up

Let another worker handle the job instead.

bugbug/repository.py

@@ -1144,7 +1144,7 @@ def pull(repo_dir: str, branch: str, revision: str) -> None:
     """Pull a revision from a branch of a remote repository into a local repository"""
 
     @tenacity.retry(
-        stop=tenacity.stop_after_attempt(3),
+        stop=tenacity.stop_after_attempt(2),
         reraise=True,
         after=tenacity.after_log(logger, logging.DEBUG),
         retry=tenacity.retry_if_exception_type(subprocess.TimeoutExpired),