Austenem/CAT-841 fix notebook download

Summary

Tiny fix for bug preventing visualization notebooks from being downloaded on dataset detail pages.

Manually tested and was able to download several notebooks successfully.

[X] Code follows the project's coding standards
- [X] Lint checks pass locally
- [X] New CHANGELOG-your-feature-name-here.md is present in the root directory, describing the change(s) in full sentences.
[ ] Unit tests covering the new feature have been added
[X] All existing tests pass
[X] Any relevant documentation in JIRA/Confluence has been updated to reflect the new feature
[X] Any new functionalities have appropriate analytics functionalities added