[python] Fix task switch set global parameter (#7693)

* [python] Fix task switch set global parameter

* Change name

dolphinscheduler-python/pydolphinscheduler/examples/task_switch_example.py

@@ -36,6 +36,14 @@ from pydolphinscheduler.tasks.switch import Branch, Default, Switch, SwitchCondi
 with ProcessDefinition(
     name="task_switch_example",
     tenant="tenant_exists",
+    param=[
+        {
+            "prop": "var",
+            "direct": "IN",
+            "type": "VARCHAR",
+            "value": "1"
+        }
+    ]
 ) as pd:
     parent = Shell(name="parent", command="echo parent")
     switch_child_1 = Shell(name="switch_child_1", command="echo switch_child_1")

dolphinscheduler-python/pydolphinscheduler/src/pydolphinscheduler/core/process_definition.py

@@ -332,7 +332,7 @@ class ProcessDefinition(Base):
             self._project,
             self.name,
             str(self.description) if self.description else "",
-            str(self.param) if self.param else None,
+            json.dumps(self.param) if self.param else None,
             json.dumps(self.schedule_json) if self.schedule_json else None,
             json.dumps(self.task_location),
             self.timeout,