fix: don't use isparameter in generate_initializesystem

Author: AayushSabharwal

src/systems/nonlinear/initializesystem.jl

@@ -214,7 +214,7 @@ function generate_initializesystem_timeindependent(sys::AbstractSystem;
     initialization_eqs = filter(initialization_eqs) do eq
         empty!(vs)
         vars!(vs, eq; op = Initial)
-        non_params = filter(!isparameter, vs)
+        non_params = filter(!in(Set(full_parameters(sys))), vs)
         # error if non-parameters are present in the initialization equations
         if !isempty(non_params)
             throw(UnknownsInTimeIndependentInitializationError(eq, non_params))