Update actions/checkout action to v3 (#27)

Co-authored-by: Renovate Bot <[email protected]>

Author: renovate[bot]

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
 
       - name: Set up JDK 8
         uses: actions/setup-java@v3