Update actions/checkout action to v6 (#19)

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

Author: renovate[bot]

.github/workflows/build.yaml

@@ -11,7 +11,7 @@ jobs:
     permissions:
       contents: write
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: set up JDK 21
         uses: actions/setup-java@v5

.github/workflows/release.yaml

@@ -10,7 +10,7 @@ jobs:
     permissions:
       contents: write
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: set up JDK 21
         uses: actions/setup-java@v5