imaplib: restore original exception msg formatting

This reduces the footprint of PR #122542.

Author: Forest

Lib/imaplib.py

@@ -379,7 +379,7 @@ def readline(self):
 
         line = b''.join(parts)
         if len(line) > _MAXLINE:
-            raise self.error(f'got more than {_MAXLINE} bytes')
+            raise self.error("got more than %d bytes" % _MAXLINE)
         return line