fix: update flutter version to the latest (#474)

Author: quekyj

.github/workflows/build_devtool.yml

@@ -22,7 +22,7 @@ jobs:
           uses: flutter-actions/setup-flutter@v2
           with:
             channel: stable
-            version: 3.16.9
+            version: 3.19.3
 
         - name: Run Flutter Test
           run: tool/gh_actions/devtool/run_devtool_test.sh

.github/workflows/general.yml

@@ -103,8 +103,8 @@ jobs:
       - name: Setup Flutter SDK
         uses: flutter-actions/setup-flutter@v2
         with:
-          channel: beta
-          version: 3.18.0-0.2.pre
+          channel: stable
+          version: 3.19.3
 
       - name: Run Flutter Test
         run: tool/gh_actions/devtool/run_devtool_test.sh