chore: Update Flutter version (#406)

Author: github-actions[bot]

.cirrus.yml

@@ -6,9 +6,9 @@ docker_builder:
     # from https://flutter.dev/docs/development/tools/sdk/releases
     matrix:
       - DOCKER_TAG: latest
-        FLUTTER_VERSION: 3.38.2
+        FLUTTER_VERSION: 3.38.3
       - DOCKER_TAG: stable
-        FLUTTER_VERSION: 3.38.2
+        FLUTTER_VERSION: 3.38.3
       - DOCKER_TAG: beta
         FLUTTER_VERSION: 3.39.0-0.1.pre
   version_script: docker --version