Bump actions/checkout from 5 to 6 (#536)

See https://github.com/actions/checkout/releases/tag/v6.0.0.

.github/workflows/lint.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v6
         with:
           python-version: "3.x"

.github/workflows/update.yml

@@ -28,12 +28,12 @@ jobs:
           path: ~/.cache
 
       - name: Clone self repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           ref: ${{ github.head_ref }}
 
       - name: Clone website repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           repository: endoflife-date/endoflife.date
           path: website