a viewset's action list gets "head" added to it, but only after being called at least once

[rtpg]

https://github.com/encode/django-rest-framework/blame/853969c69c815be69513c2f63a41285858a45352/rest_framework/viewsets.py#L106-L107

We didn't have head set in our actions on a viewset, but head would suddenly appear in a viewset's actions, but seemingly randomly.

This way of filling in head in actions means that before you call a viewset at least once, it will have one set of actions, but afterwards it would have another.

This is surprising to me, and I have a hard time imagining it to be the right solution here. But perhaps I am missing a detail.

[browniebroke]

Seems like this behaviour is due to what was done in #7223 for #6196

Do you have a suggestion on how to fix that?

[Sajadrahimi]

I guess the initial idea of changing SimpleRouter and action decorator was the better way to go with. I applied to changes here, it seems fine to me if you're fine with it I can open a PR @browniebroke .