Add NonlinearSolve v4 to test compat

This is not a direct dependency, but test-only. This release has been out for a while, not sure why CompatHelper didn't put it up.

This will allow the latest MTK release in SciML/SciMLBase.jl#922 (comment).

Author: visr

Project.toml

@@ -79,7 +79,7 @@ Markdown = "1.10"
 ModelingToolkit = "9.42"
 Mooncake = "0.4.52"
 NLsolve = "4.5.1"
-NonlinearSolve = "3.0.1"
+NonlinearSolve = "3.0.1, 4"
 Optimization = "4"
 OptimizationOptimisers = "0.3"
 OrdinaryDiffEq = "6.81.1"