Add Assign to Jsonata choices (#4130)

Author: kddejong

src/cfnlint/rules/resources/stepfunctions/StateMachineDefinition.py

@@ -78,6 +78,7 @@ def _convert_schema_to_jsonata(self):
                             "properties": {
                                 "Condition": {"type": "string"},
                                 "Next": {"pattern": "^.{1,128}$", "type": "string"},
+                                "Assign": {"type": "object"},
                             },
                             "additionalProperties": False,
                             "required": ["Condition", "Next"],