CI: cache cargo install mdbook

Author: tmandry

.github/workflows/mdbook.yml

@@ -32,11 +32,11 @@ jobs:
       MDBOOK_VERSION: 0.4.21
     steps:
       - uses: actions/checkout@v3
-      - name: Install mdBook
-        run: |
-          curl --proto '=https' --tlsv1.2 https://sh.rustup.rs -sSf -y | sh
-          rustup update
-          cargo install --version ${MDBOOK_VERSION} mdbook
+      - name: Install mdbook
+        uses: baptiste0928/cargo-install@v2
+        with:
+          crate: mdbook
+          version: "^0.4.21"
       - name: Setup Pages
         id: pages
         uses: actions/configure-pages@v3