chore(deps): update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/pkgdown.yaml

@@ -11,7 +11,7 @@ jobs:
     env:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v6
 
       - uses: actions/setup-node@v2
         with: