Mdbook > v0.4.40 has a bug (#115)

Really closes #112 

mdBook > v0.4.40 causes this bug currently.

Author: wilwade

.github/workflows/common/set-up-mdbook/action.yaml

@@ -11,7 +11,7 @@ runs:
       uses: jontze/action-mdbook@0765bef0c7c5792f93bf3ed3d487a0ca32c9da33
       with:
         token: ${{ inputs.token }}
-        mdbook-version: "~0.4.42" # Use a semver compatible string
+        mdbook-version: "0.4.40" # Use a semver compatible string
         # Optional Plugins have to be enabled
         use-linkcheck: true
         linkcheck-version: "~0.7.7"