Update CI to use mdbook-spec

.github/workflows/main.yml

@@ -3,12 +3,25 @@ on:
   pull_request:
   merge_group:
 
+env:
+  MDBOOK_VERSION: 0.4.40
+  # When updating, be sure to also update rust-lang/rust.
+  MDBOOK_SPEC_VERSION: 0.1.0
+
 jobs:
   test:
     name: Test
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@master
+    - name: Cache
+      uses: actions/cache@v4
+      with:
+        path: |
+          ~/.cargo/bin/
+          ~/.cargo/.crates.toml
+          ~/.cargo/.crates2.json
+        key: ms-${MDBOOK_SPEC_VERSION}
     - name: Update rustup
       run: rustup self update
     - name: Install Rust
@@ -19,13 +32,15 @@ jobs:
     - name: Install mdbook
       run: |
         mkdir bin
-        curl -sSL https://github.com/rust-lang/mdBook/releases/download/v0.4.14/mdbook-v0.4.14-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=bin
+        curl -sSL https://github.com/rust-lang/mdBook/releases/download/v${MDBOOK_VERSION}/mdbook-v${MDBOOK_VERSION}-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=bin
         echo "$(pwd)/bin" >> $GITHUB_PATH
     - name: Report versions
       run: |
         rustup --version
         rustc -Vv
         mdbook --version
+    - name: Install mdbook-spec
+      run: cargo install --locked mdbook-spec@${MDBOOK_SPEC_VERSION}
     - name: Run tests
       run: mdbook test
     - name: Style checks