[3.12] Add the missing f on an f-string error message in multiprocessing. (pythonGH-127462) (python#127465)

Add the missing `f` on an f-string error message in multiprocessing. (pythonGH-127462)
(cherry picked from commit 11c0109)

Co-authored-by: Gregory P. Smith <[email protected]>

Author: miss-islington

Lib/multiprocessing/connection.py

@@ -956,7 +956,7 @@ def answer_challenge(connection, authkey: bytes):
                 f'Protocol error, expected challenge: {message=}')
     message = message[len(_CHALLENGE):]
     if len(message) < _MD5ONLY_MESSAGE_LENGTH:
-        raise AuthenticationError('challenge too short: {len(message)} bytes')
+        raise AuthenticationError(f'challenge too short: {len(message)} bytes')
     digest = _create_response(authkey, message)
     connection.send_bytes(digest)
     response = connection.recv_bytes(256)        # reject large message