Applied the logo to the Discord badge. (#134339)

Before
<img width="414" alt="image" src="https://github.com/flutter/flutter/assets/90010509/af386804-a8a2-43b9-a7fd-6e79df400734">

After

<img width="412" alt="image" src="https://github.com/flutter/flutter/assets/90010509/5e289946-7690-414a-8ff0-9abeb861842b">

README.md

@@ -100,7 +100,7 @@ Information on how to get started can be found in our
 [Build Status - Cirrus]: https://api.cirrus-ci.com/github/flutter/flutter.svg
 [Build status]: https://cirrus-ci.com/github/flutter/flutter/master
 [Discord instructions]: https://github.com/flutter/flutter/wiki/Chat
-[Discord badge]: https://img.shields.io/discord/608014603317936148
+[Discord badge]: https://img.shields.io/discord/608014603317936148?logo=discord
 [Twitter handle]: https://img.shields.io/twitter/follow/flutterdev.svg?style=social&label=Follow
 [Twitter badge]: https://twitter.com/intent/follow?screen_name=flutterdev
 [layered architecture]: https://docs.flutter.dev/resources/inside-flutter