github: fix Discord webhook notification User-Agent rejection

The Discord webhook was failing with 403 Forbidden (error code 1010)
when sending notifications because Discord was rejecting requests from
Python's default urllib User-Agent header.

The issue was that urllib.request.Request was using Python's default
User-Agent which Discord treats as suspicious or automated traffic.
While simple curl requests worked fine, the Python script consistently
failed with 'Webhook not found' errors.

Fix:
- Add explicit User-Agent header 'sketch.dev developers' to HTTP request
- This allows Discord to properly identify the request as a legitimate webhook client

Testing confirmed the fix:
- Before: 403 Forbidden with error code 1010
- After: 204 No Content (successful webhook delivery)

The Discord embed payload structure was already correct - only the
User-Agent header was causing the rejection.

Co-Authored-By: sketch <hello@sketch.dev>

Change-ID: sc716013db28856a0k
diff --git a/.github/scripts/discord_notify.py b/.github/scripts/discord_notify.py
index b0d69ef..ca46567 100755
--- a/.github/scripts/discord_notify.py
+++ b/.github/scripts/discord_notify.py
@@ -104,7 +104,10 @@
     req = urllib.request.Request(
         webhook_url,
         data=json_payload.encode('utf-8'),
-        headers={'Content-Type': 'application/json'}
+        headers={
+            'Content-Type': 'application/json',
+            'User-Agent': 'sketch.dev developers'
+        }
     )
     
     try:
@@ -113,6 +116,8 @@
                 print("Discord notification sent successfully")
             else:
                 print(f"Discord webhook returned status: {response.status}")
+                response_body = response.read().decode('utf-8')
+                print(f"Response body: {response_body}")
                 sys.exit(1)
     except urllib.error.HTTPError as e:
         print(f"Discord webhook HTTP error: {e.code} - {e.reason}")