Update actions/checkout to v3 to supress the Node.js 12 deprecation

Author: mshibuya

.github/workflows/test.yml

@@ -33,7 +33,7 @@ jobs:
       EXPERIMENTAL: ${{ matrix.experimental }}
       JRUBY_OPTS: --debug
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - name: Setup ImageMagick policy
       run: sudo sh -c 'echo '\''<policymap><policy domain="coder" rights="read|write" pattern="PDF" /></policymap>'\'' > /etc/ImageMagick-6/policy.xml'
     - name: Update package list