Github Actions action

[fredrikekre]

I configured a workflow to run ExplicitImports.jl's check on CI, see Ferrite-FEM/Ferrite.jl#954. Perhaps it would be worth having this as a proper actions so that not everyone need to maintain a block like in the PR above?

[ericphanson]

Interesting, looks useful. I was thinking that getting these checks into Aqua.jl could be the “distribution” method since it’s already commonly used (and there’s probably a GitHub action for it). I don’t see any reason we couldn’t also have a direct GitHub action though.