deploy preview issues from forked branches?

[acao]

I think when a branch is from a fork, deploy previews are not appearing, perhaps?

maybe related to our choice of github actions on clause types: [opened, synchronize]

#1988 is a great example of this

[acao]

the main reason I moved to this deploy previews pattern is because I didn't want to use up all the build minutes on the shared graphql foundation netlify plan also used by graphql.org and swapi-graphql, but we do use up a ton of netlify bandwith

[acao]

we will need to move back to netlify builds I think