fix gh-pages build

Author: ukkopahis

.github/workflows/main.yml

@@ -14,5 +14,6 @@ jobs:
         with:
           python-version: 3.x
       - run: pip install mkdocs-material
+      - run: pip install mkdocs-redirects
       - run: pip install mkdocs-git-revision-date-localized-plugin
       - run: mkdocs gh-deploy --force