[flutter_releases] Flutter beta 2.9.0-0.0.pre Engine Cherrypicks (#30313)

* 'Update Dart SDK to 88bcc99a5555d1b463b9601feb6973c97846e2e2'

* 'add branch flutter-2.8-candidate.10 to enabled_branches in .ci.yaml'
diff --git a/.ci.yaml b/.ci.yaml
index ff5f3d1..55c8fca 100644
--- a/.ci.yaml
+++ b/.ci.yaml
@@ -6,6 +6,7 @@
 # More information at:
 #  * https://github.com/flutter/cocoon/blob/main/CI_YAML.md
 enabled_branches:
+  - flutter-2.8-candidate.10
   - main
   - flutter-\d+\.\d+-candidate\.\d+
 
diff --git a/DEPS b/DEPS
index 51064b2..0a691ab 100644
--- a/DEPS
+++ b/DEPS
@@ -39,7 +39,7 @@
   # 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': '68bd3305228da46d0049f6505f9cce5d453420d7',
+  'dart_revision': '88bcc99a5555d1b463b9601feb6973c97846e2e2',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py