Bump actions/download-artifact from 3 to 4 (#2)

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/docs-build.yml

@@ -20,7 +20,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4 # deploy needs git credentials
       - name: Download prepared docs
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: docs-html-${{ github.sha }}
           path: docs/build/html