Use the Flutter version specified in flutter-version.yaml for F-Droid (#2706)

builds.

Author: julien4215

.github/workflows/upload_fdroid_github.yml

@@ -18,6 +18,8 @@ jobs:
 
       - name: Install Flutter
         uses: subosito/flutter-action@v2
+        with:
+          flutter-version-file: flutter-version.yaml
       - run: flutter doctor -v
 
       - name: Checkout mobile code