remove gradle again

frontend/.github/workflows/build_app_android.yaml

@@ -1,7 +1,7 @@
 on:
   push:
-    branches:
-      - main
+    tags:
+      - 'v*'
 
 jobs:
   build:
@@ -23,6 +23,13 @@ jobs:
 
       - name: Setup android SDK
         uses: android-actions/setup-android@v3
+      
+      - name: Install Flutter
+        uses: subosito/flutter-action@v2
+        with:
+          channel: stable
+          flutter-version: 3.22.0
+          cache: true
 
       - name: Infer version number from git tag
         id: version
@@ -30,13 +37,14 @@ jobs:
           REF_NAME: ${{ github.ref_name }}
         run:
           # remove the 'v' prefix from the tag name
-          echo "VERSION=${REF_NAME//v}" >> $GITHUB_OUTPUT
+          echo "VERSION_NAME=${REF_NAME//v}" >> $GITHUB_ENV
 
       - name: Load secrets from github
         run: |
           echo "${{ secrets.ANDROID_SECRET_PROPERTIES }}" > secrets.properties
-          echo "${{ secrets.ANDROID_KEYSTORE }}" > release.keystore
           echo "${{ secrets.ANDROID_GOOGLE_PLAY_JSON }}" > google-key.json
+          # decode the base64 encoded google key
+          echo "${{ secrets.ANDROID_KEYSTORE_BASE64 }}" | base64 -d - > release.keystore
         working-directory: android
 
       - name: Install fastlane
@@ -46,5 +54,4 @@ jobs:
       - name: Run fastlane lane
         run: bundle exec fastlane deploy_testing
         working-directory: android
-        env:
-          VERSION_NAME: ${{ steps.version.VERSION }}
+        # the environment variable VERSION_NAME is implicitly available