Update retcode to == for back and forwards compatability

This might be the last thing required to fully switch to enums, SciML/SciMLBase.jl#274

Author: ChrisRackauckas

Project.toml

@@ -1,7 +1,7 @@
 name = "ModelingToolkit"
 uuid = "961ee093-0014-501f-94e3-6117800e7a78"
 authors = ["Yingbo Ma <[email protected]>", "Chris Rackauckas <[email protected]> and contributors"]
-version = "8.28.0"
+version = "8.28.1"
 
 [deps]
 AbstractTrees = "1520ce14-60c1-5f80-bbc7-55ef81b5835c"

src/structural_transformation/utils.jl

@@ -387,7 +387,7 @@ function numerical_nlsolve(f, u0, p)
     prob = NonlinearProblem{false}(f, u0, p)
     sol = solve(prob, NewtonRaphson())
     rc = sol.retcode
-    rc === :DEFAULT || nlsolve_failure(rc)
+    rc == :DEFAULT || nlsolve_failure(rc)
     # TODO: robust initial guess, better debugging info, and residual check
     sol.u
 end