Don't use a namedtuple for _Overwrites

Fix #5109

discord/abc.py

@@ -27,7 +27,6 @@ DEALINGS IN THE SOFTWARE.
 import abc
 import copy
 import asyncio
-from collections import namedtuple
 
 from .iterators import HistoryIterator
 from .context_managers import Typing
@@ -163,7 +162,22 @@ class PrivateChannel(metaclass=abc.ABCMeta):
             return NotImplemented
         return NotImplemented
 
-_Overwrites = namedtuple('_Overwrites', 'id allow deny type')
+class _Overwrites:
+    __slots__ = ('id', 'allow', 'deny', 'type')
+
+    def __init__(self, **kwargs):
+        self.id = kwargs.pop('id')
+        self.allow = kwargs.pop('allow', 0)
+        self.deny = kwargs.pop('deny', 0)
+        self.type = kwargs.pop('type')
+
+    def _asdict(self):
+        return {
+            'id': self.id,
+            'allow': self.allow,
+            'deny': self.deny,
+            'type': self.type,
+        }
 
 class GuildChannel:
     """An ABC that details the common operations on a Discord guild channel.