Update flutter version used for CI and builds

Author: rolandgeider

.github/workflows/android-release.yml

@@ -25,7 +25,7 @@ jobs:
         uses: subosito/flutter-action@v1
         with:
           channel: 'stable'
-          flutter-version: '3.0.x'
+          flutter-version: '3.3.x'
 
       - name: Decrypt config files
         run: |

.github/workflows/ci.yml

@@ -12,15 +12,15 @@ on:
       - 'pubspec.yaml'
 jobs:
   test:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     steps:  
     - uses: actions/checkout@v1
 
     - name: Install Flutter
       uses: subosito/flutter-action@v1
       with:
         channel: 'stable'
-        flutter-version: '3.0.x'
+        flutter-version: '3.3.x'
 
     - run: dart --version
     - run: flutter --version