Merge branch 'jmc-wait-formr-prepared' into 'master'

E2E tests: wait for MRs to be prepared

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/127707



Merged-by: Chloe Liu <yliu@gitlab.com>
Approved-by: Chloe Liu <yliu@gitlab.com>
Reviewed-by: Chloe Liu <yliu@gitlab.com>
Reviewed-by: John McDonnell <jmcdonnell@gitlab.com>
Reviewed-by: Jay McCure <jmccure@gitlab.com>
Co-authored-by: Jay McCure <jmccure@gitlab.com>