environment: add a setter for Variable.json (#29240)

hobo/environment/models.py

@@ -72,13 +72,17 @@ class Variable(models.Model):
                 raise ValidationError('invalid JSON document')
         return self.value
 
-    @property
-    def json(self):
+    def json_getter(self):
         try:
             return self._parse_value_as_json()
         except ValidationError:
             return self.value
 
+    def json_setter(self, value):
+        self.value = json.dumps(value)
+
+    json = property(json_getter, json_setter)
+
     def clean(self):
         self._parse_value_as_json()