Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/build-ubuntu.yml

@@ -11,7 +11,7 @@ jobs:
         java_version: [ 11, 17 ]
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: "Set up JDK ${{ matrix.java_version }}"
         uses: actions/setup-java@v5
         with:

.github/workflows/build-windows.yml

@@ -11,7 +11,7 @@ jobs:
         java_version: [ 11 ]
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: "Set up JDK ${{ matrix.java_version }}"
         uses: actions/setup-java@v5
         with: