Handle `missed:x.y` the same way as `missed-deliverable`

In !353 (merged) we updated missed-deliverable but we forgot to update ~"missed:x.y" which is required for #356 (closed)

This makes sure that we use the same logic for adding missed-deliverable and ~"missed:x.y". We always add ~"missed:x.y" when missed, and only add missed-deliverable when it's a Deliverable.

• Dry-run schedule: https://gitlab.com/gitlab-org/quality/triage-ops/pipelines/96695992

Closes #356 (closed)