Switch to non deprecated version of github actions ruby

.github/workflows/ci.yml

@@ -5,7 +5,12 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: ['2.5', '2.6', '2.7']
+        ruby:
+          - 2.3
+          - 2.4
+          - 2.5
+          - 2.6
+          - 2.7
     steps:
       - name: Check out repository code
         uses: actions/checkout@v2
@@ -17,7 +22,7 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-gem-
       - name: Set up Ruby
-        uses: actions/setup-ruby@v1
+        uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby }}
       - name: Install bundler