Fix all_channel permissions

When the new permission for send_messages_in_threads was added, we added
the wrong bit. Instead of adding the bit as the most significant (37),
we added it as the last significant, which invalidated most of the
permissions defined by this method.

discord/permissions.py

@@ -173,7 +173,7 @@ def all_channel(cls: Type[P]) -> P:
            :attr:`use_external_stickers`, :attr:`send_messages_in_threads` and
            :attr:`request_to_speak` permissions.
         """
-        return cls(0b111101101100111111011111111111010100011)
+        return cls(0b111110110110011111101111111111101010001)
 
     @classmethod
     def general(cls: Type[P]) -> P: