ref: fix subscription_id None check (#74640)

looks like this might've been skipping some of these as well (always
passing `None` when deleting)

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src/sentry/uptime/subscriptions/tasks.py

@@ -68,7 +68,7 @@ def delete_remote_uptime_subscription(uptime_subscription_id, **kwargs):
         subscription.update(subscription_id=None)
 
     if subscription_id is not None:
-        send_uptime_config_deletion(subscription.subscription_id)
+        send_uptime_config_deletion(subscription_id)
 
 
 def send_uptime_subscription_config(subscription: UptimeSubscription) -> str: