workflows: Don't try to upload when running in someone's fork

[jepler]

.. which we can tell by whether the environment variable is non-empty.

This fixes a problem where, when I push to my own circuitpython fork, which has actions enabled, I eventually get a failure at the upload step. See e.g., https://github.com/jepler/circuitpython/commit/8e9ac593963537f2504efdfeefe28782de68a53f/checks?check_suite_id=315428254 where all board builds fail at the upload step.

This may only affect users who have deliberately enabled actions within their fork, or maybe actions are still a beta/opt in thing at the user level? For instance, checking another random fork that has recently prepared a pull request, there are no actions that ran in the past: https://github.com/sarfata/circuitpython/actions

[dhalbert]

This may only affect users who have deliberately enabled actions within their fork, or maybe actions are still a beta/opt in thing at the user level?

I don't have this problem, but I don't have actions enabled on my fork.

[dhalbert]

Thanks for this!