Resolve "ActionView::Template::Error: IpynbDiff::InvalidTokenError"

Sentry error: https://sentry.gitlab.net/gitlab/gitlabcom/issues/3204685/?query=is%3Aunresolved%20%22IpynbDiff%3A%3AInvalidTokenError%22

!75500 (merged) introduced this error through the new version of https://gitlab.com/gitlab-org/incubation-engineering/mlops/rb-ipynbdiff, but it is affecting a very small number of users and it is hard to reproduce. For now, when this error appears, we will fallback to raw diffs, and we do when the notebook in itself is invalid, and continue to log the errors.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #353558 (closed)