Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/build-test.yml

@@ -6,7 +6,7 @@ jobs:
     name: Build with Java 8
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-java@v5
         with:
           java-version: "8"

.github/workflows/release.yml

@@ -12,7 +12,7 @@ jobs:
       contents: write
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Setup Java 8
         uses: actions/setup-java@v5.0.0
         with: