some more adjustments

frontend/.github/workflows/build_app_ios.yaml

@@ -5,15 +5,18 @@ on:
 
 jobs:
   build:
-    runs-on: macos-15
+    runs-on: macos-latest
+    env:
+      # $BUNDLE_GEMFILE must be set at the job level, so it is set for all steps
+      BUNDLE_GEMFILE: ios/Gemfile
     steps:
       - uses: actions/checkout@v4
 
       - name: Set up ruby env
         uses: ruby/setup-ruby@v1
         with:
-          ruby-version: 3.2.1
-          bundler-cache: true
+          ruby-version: 3.3
+          bundler-cache: true # runs 'bundle install' and caches installed gems automatically
 
       - name: Install Flutter
         uses: subosito/flutter-action@v2
@@ -39,10 +42,6 @@ jobs:
         env:
           MATCH_REPO_SSH_KEY: ${{ secrets.IOS_MATCH_REPO_SSH_KEY_BASE64 }}
 
-      - name: Install fastlane
-        run: bundle install
-        working-directory: ios
-
       - name: Install dependencies and clean up
         run: |
           flutter pub get