ci: move book generation testing into same workflow

.github/workflows/book.yml

@@ -1,20 +0,0 @@
-name: Build book
-on:
-  push:
-jobs:
-  deploy:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - name: Setup mdBook
-        uses: peaceiris/actions-mdbook@v1
-        with:
-          mdbook-version: 'latest'
-      - run: mdbook build book
-      - run: cp book/404.html book/book/
-      - name: Deploy
-        uses: peaceiris/actions-gh-pages@v3
-        if: ${{ github.ref == 'refs/heads/main' }}
-        with:
-          github_token: ${{ secrets.GITHUB_TOKEN }}
-          publish_dir: ./book/book

.github/workflows/rust.yml

@@ -87,3 +87,12 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: EmbarkStudios/cargo-deny-action@v1
+
+  Book:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: taiki-e/install-action@v2
+        with:
+          tool: mdbook
+      - run: mdbook build book