Invalidate markdown cache to clear up stored XSS
This is a follow up to https://gitlab.com/gitlab-org/gitlab/-/issues/440503, where it is showed that XSS payload which was used for validating the stored XSS issue (https://gitlab.com/gitlab-org/gitlab/-/issues/431201) when it was originally reported stills gets executed. It looks like XSS payload was cached and the markdown needs to be invalidated similar to https://gitlab.com/gitlab-org/security/gitlab/-/merge_requests/2387.
Edited by Nikhil George