added missing enum (Azure#17828)

Author: jorgecotillo

specification/resources/resource-manager/Microsoft.Resources/preview/2022-03-01-preview/changes.json

@@ -308,7 +308,8 @@
           "readOnly": true,
           "enum": [
             "User",
-            "System"
+            "System",
+            "Create"
           ],
           "x-ms-enum": {
             "name": "ChangeCategory",