install bundlern when needed

.gitea/workflows/frontend_build-app-ios.yaml

@@ -29,6 +29,12 @@ jobs:
           architecture: x64
           cache: true
 
+      - name: Set up ruby env
+        uses: https://github.com/ruby/setup-ruby@v1
+        with:
+          ruby-version: 3.3
+          bundler-cache: true # runs 'bundle install' and caches installed gems automatically
+
       - name: Install dependencies and clean up
         run: |
           flutter pub get
@@ -36,12 +42,6 @@ jobs:
           flutter clean
           bundle exec pod cache clean --all
 
-      - name: Set up ruby env
-        uses: https://github.com/ruby/setup-ruby@v1
-        with:
-          ruby-version: 3.3
-          bundler-cache: true # runs 'bundle install' and caches installed gems automatically
-
       - name: Fetch tags from main branch
         # since this workflow is triggered by a pull request, we want to match the latest tag of the main branch
         id: build_name