Fix missing plugin from ci.yml

Author: zlovatt

.github/workflows/ci.yml

@@ -28,5 +28,5 @@ jobs:
           path: .cache
           restore-keys: |
             mkdocs-material-
-      - run: pip install mkdocs-material mkdocs-git-revision-date-localized-plugin
+      - run: pip install mkdocs-material mkdocs-git-revision-date-localized-plugin mkdocs-print-site-plugin
       - run: mkdocs gh-deploy --force