update workflow file

Author: stm7128

.github/workflows/mozc-ut.yaml

@@ -26,9 +26,9 @@ jobs:
         path: merge-ut-dictionaries-win
 
     - name: Set up Ruby
-      uses: actions/setup-ruby@v1
+      uses: ruby/setup-ruby@v1
       with:
-        ruby-version: 2.7
+        bundler-cache: true
 
     - name: make UT dic
       shell: cmd