Don't use Bulk Channel Edit endpoint if not actually moving channels.

Should make the category-only edit cases more straightforward since
it does not rely on other guilds in the cache, outside of the category
itself.

discord/abc.py

@@ -239,7 +239,10 @@ class GuildChannel:
             position = options.pop('position')
         except KeyError:
             if parent_id is not _undefined:
-                yield from self._move(self.position, parent_id=parent_id, lock_permissions=lock_permissions, reason=reason)
+                if lock_permissions:
+                    category = self.guild.get_channel(parent_id)
+                    options['permission_overwrites'] = [c._asdict() for c in category._overwrites]
+                options['parent_id'] = parent_id
             elif lock_permissions and self.category_id is not None:
                 # if we're syncing permissions on a pre-existing channel category without changing it
                 # we need to update the permissions to point to the pre-existing category

discord/http.py

@@ -500,7 +500,7 @@ class HTTPClient:
 
     def edit_channel(self, channel_id, *, reason=None, **options):
         r = Route('PATCH', '/channels/{channel_id}', channel_id=channel_id)
-        valid_keys = ('name', 'topic', 'bitrate', 'nsfw', 'user_limit', 'position', 'permission_overwrites')
+        valid_keys = ('name', 'parent_id', 'topic', 'bitrate', 'nsfw', 'user_limit', 'position', 'permission_overwrites')
         payload = {
             k: v for k, v in options.items() if k in valid_keys
         }