Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/build-test.yml

@@ -18,7 +18,7 @@ jobs:
     permissions:
       contents: read
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v6
       - uses: actions/setup-java@v3
         with:
           java-version: "17"