Test older mdbook version

Author: jvsguerra

.github/workflows/mdbook.yml

@@ -29,7 +29,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     env:
-      MDBOOK_VERSION: 0.4.49
+      MDBOOK_VERSION: 0.4.28
     steps:
       - uses: actions/checkout@v5
       - name: Install mdBook