TODO: Run GHA on Julia 1.5, 1.6-nightly, and nightly
Created by: DilumAluthge
Currently, we run GitHub Actions on the following versions of Julia:
1.5
nightly
We should instead run GitHub Actions on the following versions of Julia:
1.5
1.6-nightly
nightly
We'll need to fix https://github.com/julia-actions/setup-julia/issues/65 first.