Update actions/checkout action to v4 (#31)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
       matrix:
         java: [ '1.8', '11', '17' ]
     steps:
-      - uses: actions/checkout@v3.6.0
+      - uses: actions/checkout@3df4ab11eba7bda6032a0b82a6bb43b11571feac # v4.0.0
         with:
           fetch-depth: 100
       - name: Fetch tags