docs: Make update-user-group use curl example system.

templates/zerver/api/update-user-group.md

@@ -13,12 +13,7 @@ Update the name or description of a [user group](/help/user-groups).
 
 {tab|curl}
 
-``` curl
-curl -X PATCH {{ api_url }}/v1/user_groups/42 \
-    -u BOT_EMAIL_ADDRESS:BOT_API_KEY \
-    -d 'name="marketing"' \
-    -d 'description="The marketing team."'
-```
+{generate_code_example(curl)|/user_groups/{group_id}:patch|example}
 
 {end_tabs}
 

zerver/openapi/test_curl_examples.py

@@ -25,6 +25,7 @@ exclude_list = [
     'delete-stream.md',
     'get-presence.md',
     'create-user-group.md',
+    'update-user-group.md',
     # Endpoint can be called only by administrators.
     'create-user.md',
     # Endpoint does not accept bot requests