Merge branch '377825-integrations-zentao-update-removal_milestone' into 'master'

Change removal milestone of ZenTao to 18.0

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/153783



Merged-by: Evan Read <eread@gitlab.com>
Approved-by: Evan Read <eread@gitlab.com>
Co-authored-by: Luke Duncalfe <lduncalfe@eml.cc>