Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/upgrade-lucide.yml

@@ -21,7 +21,7 @@ jobs:
 
     steps:
     - name: Checkout repository (full history)
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         fetch-depth: 0
         token: ${{ secrets.GITHUB_TOKEN }}