fix: unwrap substitution rules in `nlstep=true`#3877

ChrisRackauckas merged 1 commit intoSciML:masterSciML/ModelingToolkit.jl:masterfrom

AayushSabharwal:as/fix-ode-nlstepAayushSabharwal/ModelingToolkit.jl:as/fix-ode-nlstepCopy head branch name to clipboard