Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/builder.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Set up QEMU
       uses: docker/setup-qemu-action@v3

.github/workflows/validate.yml

@@ -11,7 +11,7 @@ jobs:
 
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         fetch-depth: '0'