Don't store a user cache if there's no member intent or cache is off

Without a cache or member intent the user cache can get out of date
with no events to update the underlying user in the member object.

Ref: #6034

discord/flags.py

@@ -851,6 +851,10 @@ class MemberCacheFlags(BaseFlags):
         self.value = self.DEFAULT_VALUE
         return self
 
+    @property
+    def _empty(self):
+        return self.value == self.DEFAULT_VALUE
+
     @flag_value
     def online(self):
         """:class:`bool`: Whether to cache members with a status.

discord/state.py

@@ -186,6 +186,9 @@ class ConnectionState:
         self._status = status
         self._intents = intents
 
+        if not intents.members or cache_flags._empty:
+            self.store_user = self.store_user_no_intents
+
         self.parsers = parsers = {}
         for attr, func in inspect.getmembers(self):
             if attr.startswith('parse_'):
@@ -279,6 +282,9 @@ class ConnectionState:
                 self._users[user_id] = user
             return user
 
+    def store_user_no_intents(self, data):
+        return User(state=self, data=data)
+
     def get_user(self, id):
         return self._users.get(id)