Fix pkg.pr.new releases only on PRs to main, and commits to main

[nathanclevenger]

I think right now it's all commits, as well as PRs, so it's release twice. We want to release if committing directly to main, or merging a PR to main, but we don't ever need 2 releases to run at the same time

[linear]

MDX-24 Fix pkg.pr.new releases only on PRs to main, and commits to main