move activity task starter into 'on_ready' event

it was being started before the bot websocket was established

cogs/activity.py

@@ -19,7 +19,11 @@ class ActivityCog(commands.Cog):
     """
     def __init__(self, bot: commands.Bot):
         self.bot = bot
-        self.update_activity.start()
+
+    @commands.Cog.listener()
+    async def on_ready(self):
+        if not self.update_activity.is_running():
+            self.update_activity.start()
 
     @tasks.loop(seconds=30)
     async def update_activity(self):