Roll Dart SDK from 6c4eb86ecd25 to c2a455113e39 (1 revision) (#46317)

https://dart.googlesource.com/sdk.git/+log/6c4eb86ecd25..c2a455113e39

2023-09-27 dart-internal-merge@dart-ci-internal.iam.gserviceaccount.com Version 3.2.0-203.0.dev

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/dart-sdk-flutter-engine
Please CC dart-vm-team@google.com,jacksongardner@google.com on the revert to ensure that a human
is aware of the problem.

To file a bug in Flutter Engine: https://github.com/flutter/flutter/issues/new/choose

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

Author: skia-flutter-autoroll

DEPS

@@ -57,7 +57,7 @@ vars = {
   # 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': '6c4eb86ecd258fac93e87ef47812c5a8e1899411',
+  'dart_revision': 'c2a455113e39a3cbc73e262fd66520e0e6a04a26',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py