Make adding new gitlab milestones part of the release process
For main releases, if the release is
5.n.0 suggest to create:
5.n.1milestone. Example for 5.33.0, create a 5.33.1 milestone.
5.(n+2).0milestone. Example for 5.33.0 create a 5.35.0 milestone. There will already be a 5.34.0 milestone from the previous release.
For smaller releases, e.g. 5.33.1, it's optional based on timing. If it's early in the cycle then could make the next point milestone, e.g. 5.33.2.
This isn't a huge problem, it's just that every month there's several tickets closed shortly after a release and there's no appropriate milestone available.