Add ruby v3.0 for pull request CI (#211)

Author: toduq

.github/workflows/pull_request.yml

@@ -7,11 +7,11 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: [ '2.4', '2.5', '2.6', '2.7' ]
+        ruby: [ '2.4', '2.5', '2.6', '2.7', '3.0' ]
     name: Ruby v${{ matrix.ruby }}
     steps:
     - uses: actions/checkout@v2
-    - uses: actions/setup-ruby@v1
+    - uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}
     - run: gem install bundler