Roll Dart SDK from 72923798f84b to 4a239aa9685f (1 revision) (#36678)

diff --git a/DEPS b/DEPS
index 6cfcd35..9c5789e 100644
--- a/DEPS
+++ b/DEPS
@@ -43,7 +43,7 @@
   # 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': '72923798f84bf92d7480870d89ba88fc497d1abb',
+  'dart_revision': '4a239aa9685fb7351193224be0a9be71ecf151c8',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py