Fix CI workflows: add Julia setup for Runic, disable downgrade tests#88

ChrisRackauckas merged 2 commits intoSciML:masterSciML/ODEInterfaceDiffEq.jl:masterfrom

ChrisRackauckas-Claude:fix-ci-workflowsChrisRackauckas-Claude/ODEInterfaceDiffEq.jl:fix-ci-workflowsCopy head branch name to clipboard