build: lower minimum MTK version

Author: SebastianM-C

Project.toml

@@ -25,7 +25,7 @@ DataInterpolations = "4.6, 5, 6"
 DiffEqBase = "6.152"
 IfElse = "0.1"
 LinearAlgebra = "1.10"
-ModelingToolkit = "9.29"
+ModelingToolkit = "9.28"
 OrdinaryDiffEq = "6.87"
 SafeTestsets = "0.1"
 Symbolics = "5.35.1, 6"