GitHub Actions "publish" job should not run on PR builds or from repo forks

[sirosen]

Describe the bug

I've noticed failures of the "publish" job (and therefore apparently "failing" CI) on my fork and on my PR builds.
These will always fail, and it would be better to skip the job in these contexts to get clearer feedback.

I believe that the job should be guarded with an if that looks to make sure it's running on funcx-faas/funcX@main.
The GitHub env vars and workflow expression language should make this possible.

To Reproduce

1. Fork the repo
2. Create a new branch off of main with no changes
3. Push to your fork
4. GitHub will email you a build failure

Expected behavior

Since the new branch is taken off of main, you would expect a passing build.