fix(ci): install rust before installing mdbook

.forgejo/workflows/botbook.yaml

@@ -17,6 +17,11 @@ jobs:
 
       - uses: actions/checkout@v4
 
+      - name: Install Rust
+        run: |
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain stable --profile minimal
+          echo "$HOME/.cargo/bin" >> $GITHUB_PATH
+
       - name: Install mdBook
         run: |
           if ! command -v mdbook &> /dev/null; then