Update dependabot.yml to ignore all jupyter-book updates

Co-authored-by: elcorto <13417423+elcorto@users.noreply.github.com>

Author: Copilot

.github/dependabot.yml

@@ -6,9 +6,8 @@ updates:
   schedule:
     interval: "weekly"
   ignore:
-    # See doc/requirements.txt for why
+    # Prevent any updates to jupyter-book (see doc/requirements.txt for why)
     - dependency-name: "jupyter-book"
-      update-types: ["version-update:semver-major"]
 
 - package-ecosystem: "github-actions"
   directory: "/"