Add mdbook-mermaid back to CI

Author: tmandry

.github/workflows/deploy.yml

@@ -13,6 +13,9 @@ jobs:
       - uses: taiki-e/cache-cargo-install-action@v2
         with:
           tool: mdbook@0.5.3
+      - uses: taiki-e/cache-cargo-install-action@v2
+        with:
+          tool: mdbook-mermaid@0.17.0
       - name: Install mdbook-linkcheck
         uses: baptiste0928/cargo-install@v3
         # Temporarily pull the fix for https://github.com/Michael-F-Bryan/mdbook-linkcheck/pull/98