[flutter_releases] Flutter beta 3.20.0-1.2.pre Engine Cherrypicks (#50836)

# Flutter beta 3.20.0-1.2.pre Engine

## Scheduled Cherrypicks

- Roll dart revision: dart-lang/sdk@08af7ffa3
diff --git a/DEPS b/DEPS
index c738c2a..b401642 100644
--- a/DEPS
+++ b/DEPS
@@ -62,7 +62,7 @@
   # Dart is: https://github.com/dart-lang/sdk/blob/main/DEPS
   # You can use //tools/dart/create_updated_flutter_deps.py to produce
   # updated revision list of existing dependencies.
-  'dart_revision': '5a5d4c2622007c10ed6adcd5787eb3a69dd8ada4',
+  'dart_revision': '08af7ffa3908badf340e2e2444ce429039196188',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py