build: upper bound SymbolicUtils to <1.6

Author: AayushSabharwal

Project.toml

@@ -105,7 +105,7 @@ SparseArrays = "1"
 SpecialFunctions = "0.7, 0.8, 0.9, 0.10, 1.0, 2"
 StaticArrays = "0.10, 0.11, 0.12, 1.0"
 SymbolicIndexingInterface = "0.3.12"
-SymbolicUtils = "1.0"
+SymbolicUtils = "<1.6"
 Symbolics = "5.26"
 URIs = "1"
 UnPack = "0.1, 1.0"