Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/gradle-build.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     if: "!contains(github.event.commits[0].message, '[ci-skip]')"
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - uses: gradle/actions/wrapper-validation@v5
     - name: Set up JDK 21
       uses: actions/setup-java@v5

.github/workflows/publish.yml

@@ -10,7 +10,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: gradle/actions/wrapper-validation@v5
       - name: Set up JDK 21
         uses: actions/setup-java@v5
@@ -33,7 +33,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Downloading artifact
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - uses: thecodemonkey/action-get-gradle-version@master
         id: version
         with:
@@ -53,7 +53,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - uses: thecodemonkey/action-get-gradle-version@master
         id: version