ci: use ruby v4

Author: KazuCocoa

.github/workflows/functional-test.yml

@@ -60,7 +60,7 @@ jobs:
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:
-        ruby-version: 3.3
+        ruby-version: 4.0
     - run: |
         bundle install
         rake ios