ci: pin mdbook to 0.4 for now, properly install mdbook-tabs (#5632)

Author: davidhewitt

.github/workflows/netlify-build.yml

@@ -31,7 +31,7 @@ jobs:
       - name: Setup mdBook
         uses: taiki-e/install-action@v2
         with:
-          tool: mdbook, mdbook-linkcheck, lychee
+          tool: mdbook@0.4, mdbook-tabs@0.2, lychee
 
       - name: Prepare tag
         id: prepare_tag