Add mergeability check for scheduled merge

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/165099



Merged-by: Kerri Miller <kerrizor@kerrizor.com>
Approved-by: mo khan <mo@mokhan.ca>
Approved-by: Amy Qualls <aqualls@gitlab.com>
Approved-by: Kerri Miller <kerrizor@kerrizor.com>
Reviewed-by: Kerri Miller <kerrizor@kerrizor.com>
Reviewed-by: Amy Qualls <aqualls@gitlab.com>
Reviewed-by: mo khan <mo@mokhan.ca>
Co-authored-by: Niklas <mc.taucher2003@gmail.com>