fix(implement:ForumChannels): Fixed crash when post get deleted

Author: mccoderpy

discord/channel.py

@@ -1919,6 +1919,9 @@ def __init__(self, *, state, guild, data) -> None:
     def _add_thread(self, thread: ThreadChannel) -> None:
         self._posts[thread.id] = thread
 
+    def _remove_thread(self, thread: ThreadChannel) -> None:
+        self._posts.pop(thread.id, None)
+
 
 class PartialMessageable(abc.Messageable, Hashable):
     """Represents a partial messageable to aid with working messageable channels when