[CI] xgrammar structured output supports Enum. (#15757)

Signed-off-by: chaunceyjiang <chaunceyjiang@gmail.com>

tests/v1/structured_output/test_utils.py

@@ -13,10 +13,6 @@ def unsupported_string_schemas():
             "type": "string",
             "pattern": "^[a-zA-Z]+$"
         },
-        {
-            "type": "string",
-            "enum": ["active", "inactive", "pending"]
-        },
         {
             "type": "string",
             "minLength": 1
@@ -164,6 +160,10 @@ def supported_schema():
                     "type": "number"
                 }
             },
+            "car_type": {
+                "type": "string",
+                "enum": ["sedan", "suv", "truck"]
+            },
             "address": {
                 "type": "object",
                 "properties": {