statuspage: Raise AnomalousWebhookPayloadError on other events.

Their documentation only describes these two event types.

zerver/webhooks/statuspage/tests.py

@@ -43,3 +43,13 @@ class StatuspageHookTests(WebhookTestCase):
             expected_message,
             content_type="application/x-www-form-urlencoded",
         )
+
+    def test_statuspage_anomalous_payload(self) -> None:
+        result = self.client_post(
+            self.url,
+            {},
+            content_type="application/json",
+        )
+        self.assert_json_error(
+            result, "Unable to parse request: Did Statuspage generate this event?", 400
+        )

zerver/webhooks/statuspage/view.py

@@ -2,7 +2,7 @@
 from django.http import HttpRequest, HttpResponse
 
 from zerver.decorator import webhook_view
-from zerver.lib.exceptions import UnsupportedWebhookEventTypeError
+from zerver.lib.exceptions import AnomalousWebhookPayloadError
 from zerver.lib.response import json_success
 from zerver.lib.typed_endpoint import JsonBodyPayload, typed_endpoint
 from zerver.lib.validator import WildValue, check_string
@@ -69,7 +69,7 @@ def api_statuspage_webhook(
         topic = get_component_topic(payload)
         body = get_components_update_body(payload)
     else:
-        raise UnsupportedWebhookEventTypeError("unknown-event")
+        raise AnomalousWebhookPayloadError
 
     check_send_webhook_message(request, user_profile, topic, body, event)
     return json_success(request)