Create actual nightly release when pushing to master

[Daxtorim]

The artifacts from Github Actions are only kept for a limited time.
You need to be logged into Github to download any artifacts.
You need to know how that page even works in the first place to find anything.

This creates an actual release when changes are pushed/merged to master. It still only builds and uploads artifacts for pull requests.
Looks like this: https://github.com/Daxtorim/polonium/releases

[zeroxoneafour]

Lgtm, thank you for doing this. I don't really know how GitHub actions work (first time using them in a project), so this is very helpful!