Quarantined e2e test slack report is broken - should be deprecated

https://gitlab.com/gitlab-org/quality/toolbox/-/jobs/10853884596#L55

I suspect it is due to the report being over 40,000 characters.

https://api.slack.com/changelog/2018-04-truncating-really-long-messages

On August 12, 2018 we started truncating messages containing more than 40,000 characters.

quarantine_report.json has 47K chars