Updating the banner (#12671)

Promoting the live stream

---------

Co-authored-by: Parker Lougheed <[email protected]>

Author: sfshaza2

src/data/banner.yml

@@ -1,7 +1,7 @@
 text: >-
-  Build high quality, feature-rich apps with
-  the new Flutter Extension for Gemini CLI.
+  Don't miss the live Flutter and Dart
+  live Q & A happening Wednesday, Nov 12 at 11am PST.
 link:
-  text: "Learn more"
-  url: "https://blog.flutter.dev/meet-the-flutter-extension-for-gemini-cli-f8be3643eaad"
+  text: "Be there!"
+  url: "https://www.youtube.com/watch?v=RTb3gP4p5bw"
   newTab: true