send_email: Define variable typed as a Union.

Signed-off-by: Zixuan James Li <p359101898@gmail.com>

zerver/lib/send_email.py

@@ -7,7 +7,7 @@ from email.headerregistry import Address
 from email.parser import Parser
 from email.policy import default
 from email.utils import formataddr, parseaddr
-from typing import Any, Dict, List, Mapping, Optional, Sequence, Tuple
+from typing import Any, Dict, List, Mapping, Optional, Sequence, Tuple, Union
 
 import backoff
 import orjson
@@ -266,7 +266,7 @@ def send_email(
     if request is not None:
         cause = f" (triggered from {request.META['REMOTE_ADDR']})"
 
-    logging_recipient = mail.to
+    logging_recipient: Union[str, List[str]] = mail.to
     if realm is not None:
         logging_recipient = f"{mail.to} in {realm.string_id}"