just download pre-built binaries instead of compiling them on the VM

.github/install-mdbook

@@ -0,0 +1,21 @@
+#!/bin/sh
+
+set -o errexit
+set -o nounset
+
+# Assume the environment variables MDBOOK_VERSION and MDBOOK_ADMONISH_VERSION are set
+
+# Download a tar ball and then unpack it into a destination
+# Arguments
+#   1 - URL for the .tar.gz to download
+#   2 - target directory to unpack into
+download() {
+  wget -q -O - "${1}" | tar -xz --directory "${2}"
+}
+
+download \
+  https://github.com/rust-lang/mdBook/releases/download/v${MDBOOK_VERSION}/mdbook-v${MDBOOK_VERSION}-x86_64-unknown-linux-gnu.tar.gz \
+  ~/.local/bin
+download \
+  https://github.com/tommilligan/mdbook-admonish/releases/download/v${MDBOOK_ADMONISH_VERSION}/mdbook-admonish-v${MDBOOK_ADMONISH_VERSION}-x86_64-unknown-linux-gnu.tar.gz \
+  ~/.local/bin

.github/workflows/mdbook.yml

@@ -34,20 +34,8 @@ jobs:
       MDBOOK_ADMONISH_VERSION: 1.19.0 # need to re-run mdbook-admonish install if updating version
     steps:
       - uses: actions/checkout@v4
-      - uses: actions/cache@v4
-        with:
-          path: |
-            ~/.cargo/bin/
-            ~/.cargo/registry/index/
-            ~/.cargo/registry/cache/
-            ~/.cargo/git/db/
-          key: ${{ runner.os }}-cargo-${{ env.MDBOOK_VERSION }}-${{ env.MDBOOK_ADMONISH_VERSION }}
       - name: Install mdBook
-        run: |
-          curl --proto '=https' --tlsv1.2 https://sh.rustup.rs -sSf -y | sh
-          rustup update
-          cargo install --version ${MDBOOK_VERSION} --locked mdbook
-          cargo install --version ${MDBOOK_ADMONISH_VERSION} --locked mdbook-admonish
+        run: ./.github/install-mdbook
       - name: Setup Pages
         id: pages
         uses: actions/configure-pages@v5