Using the new `[sources]` section in the Project.toml file to allow usage of unregistred packages.

[favba]

Would it be possible to make this GitHub action work with unregistered packages for julia v1.11 using the new [sources] section of the Project.toml file?

[lgoettgens]

I am not sure which change made this work, but it does work now (provided that you run setup-julia beforehand with julia 1.11 or newer).