Bug on labels serialization on webhook note payloads

Summary

We receive some webhook note payloads with some regressions on labels property.

What is the current bug behavior?

We receive some note payloads with some badly serialized labels.

{"object_kind":"note","event_type":"note","user":<...>,"labels":"#<Label::ActiveRecord_Associations_CollectionProxy:0x00007f766c48eb78>"}}

What is the expected correct behavior?

{"object_kind":"note","event_type":"note","user":<...>,"labels":["LIST","OF","LABELS"]}}

Output of checks

This bug happens on GitLab.com