So that each version of Ruby on CI can bundle proper gemset

Author: amatsuda

.github/workflows/main.yml

@@ -25,6 +25,8 @@ jobs:
     steps:
       - uses: actions/checkout@v3
 
+      - run: rm Gemfile.lock
+
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby-version }}