Update actions/checkout action to v6 (#286)

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

Author: renovate[bot]

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
 
     steps:
       - name: Check out the repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Install JDK
         uses: actions/setup-java@v5

.github/workflows/release.yml

@@ -11,7 +11,7 @@ jobs:
 
     steps:
       - name: Check out the repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Install JDK
         uses: actions/setup-java@v5