ci: run Taskcluster tasks on all branches

[ahal]

No description provided.

[lissyx]

Looks fine but any push to any branch will trigger build, that makes me uneasy, can we keep those branches but allow PR events? Or are things not ready yet?

[ahal]

I'm not sure why pushes to branches make you uneasy but events on PRs doesn't.. I assume they would both generate roughly the same number of tasks (pushes probably even less because many people are likely pushing to a fork).

Anyway, PRs are close.. maybe I can wrap them up today. I agree we don't really need this once we have PR events, so I can just abandon this.

[lissyx]

I dislike the practice of directly pushing to the repo. We did it for now because private repo and credentials management on GitHub actions forced us to, but I wish we can soon all send PRs from our forks instead and sanctuarize the main repo and it's branch.