fix(destinations): Handle unicode characters in webhook notifications (#7586)

* fix(destinations): Handle unicode characters in webhook notifications

Previously, webhook notifications would fail if they contained unicode characters in the alert data. This was because the JSON payload was not UTF-8 encoded before being sent.

This commit fixes the issue by explicitly encoding the JSON data to UTF-8 and adds a test to verify the fix.

* move test function to new file

---------

Co-authored-by: gaojingyu <gaojingyu>

tests/destinations/test_webhook.py

@@ -0,0 +1,50 @@
+import json
+from unittest import mock
+
+from redash.destinations.webhook import Webhook
+from redash.models import Alert
+
+
+def test_webhook_notify_handles_unicode():
+    # Create a mock alert with all the properties needed by serialize_alert
+    alert = mock.Mock()
+    alert.id = 1
+    alert.name = "Test Alert"
+    alert.custom_subject = "Test Subject With Unicode: 晨"
+    alert.custom_body = "Test Body"
+    alert.options = {}
+    alert.state = "ok"
+    alert.last_triggered_at = None
+    alert.updated_at = "2025-12-02T08:00:00Z"
+    alert.created_at = "2025-12-02T08:00:00Z"
+    alert.rearm = None
+    alert.query_id = 10
+    alert.user_id = 20
+
+    query = mock.Mock()
+    user = mock.Mock()
+    app = mock.Mock()
+    host = "http://redash.local"
+    options = {"url": "https://example.com/webhook", "username": "user", "password": "password"}
+    metadata = {}
+    new_state = Alert.TRIGGERED_STATE
+    destination = Webhook(options)
+
+    with mock.patch("redash.destinations.webhook.requests.post") as mock_post:
+        mock_response = mock.Mock()
+        mock_response.status_code = 200
+        mock_post.return_value = mock_response
+
+        destination.notify(alert, query, user, new_state, app, host, metadata, options)
+
+        # Get the data passed to the mock
+        call_args, call_kwargs = mock_post.call_args
+        sent_data = call_kwargs["data"]
+
+        # 1. Make sure we send bytes
+        assert isinstance(sent_data, bytes)
+
+        # 2. Make sure the bytes are the correct UTF-8 encoded JSON
+        decoded_data = json.loads(sent_data.decode("utf-8"))
+        assert decoded_data["alert"]["title"] == alert.custom_subject
+        assert "Test Subject With Unicode: 晨" in sent_data.decode("utf-8")