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
@@ -35,8 +42,9 @@ jobs:
       - 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
+          base64 -d ${{ secrets.ANDROID_KEYSTORE_BASE64 }} > release.keystore
         working-directory: android
 
       - name: Install fastlane