Pin mdbook to what seems to be a functional version for this

Author: rustprooflabs

.github/workflows/deploy-book.yml

@@ -6,6 +6,7 @@ on:
   push:
     branches:
       - main
+      - fix-book
 
 jobs:
   deploy:
@@ -20,7 +21,7 @@ jobs:
         echo "PATH=$HOME/.cargo/bin:$PATH" >> $GITHUB_ENV
     - name: Install mdbook
       run: |
-        cargo install mdbook
+        cargo install mdbook --version 0.4.32
     - name: Deploy GitHub Pages
       run: |
         # This assumes your book is in the root of your repository.