Fix small type annotation bug

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

board/utils.py

@@ -1,4 +1,4 @@
-from typing import TYPE_CHECKING
+from typing import Optional, TYPE_CHECKING
 from django.utils import timezone
 import ipaddress
 
@@ -33,7 +33,7 @@ def get_ip_bans(ip: str) -> list:
     return bans
 
 
-def is_banned(ip: str, board: "Board" | None) -> bool:
+def is_banned(ip: str, board: Optional["Board"]) -> bool:
     now = timezone.now()
     bans = [ban for ban in get_ip_bans(ip) if ban.board == board or not ban.board]
     if bans: