[BugFix] Fixes Qwen3-Next enable nz accuracy problem (#4058)

### What this PR does / why we need it?
- Fixes Qwen3-Next enable nz accuracy problem

### Does this PR introduce _any_ user-facing change?
N/A


- vLLM version: v0.11.0
- vLLM main:
83f478bb19

---------

Signed-off-by: Icey <1790571317@qq.com>
Signed-off-by: wxsIcey <1790571317@qq.com>

tests/ut/test_utils.py

@@ -46,12 +46,18 @@ class TestUtils(TestBase):
             self.assertFalse(utils.is_310p())
 
     def test_is_enable_nz(self):
-        with mock.patch("vllm_ascend.utils.envs_ascend.VLLM_ASCEND_ENABLE_NZ",
-                        1):
-            self.assertTrue(utils.is_enable_nz())
-        with mock.patch("vllm_ascend.utils.envs_ascend.VLLM_ASCEND_ENABLE_NZ",
-                        0):
-            self.assertFalse(utils.is_enable_nz())
+        # Case when _ENABLE_NZ is already set
+        utils._ENABLE_NZ = True
+        self.assertTrue(utils.is_enable_nz())
+
+        utils._ENABLE_NZ = False
+        self.assertFalse(utils.is_enable_nz())
+
+        # Case when _ENABLE_NZ is None and vllm_config is not provided
+        utils._ENABLE_NZ = None
+        with self.assertRaises(ValueError) as context:
+            utils.is_enable_nz()
+        self.assertIn("vllm_config must be provided", str(context.exception))
 
     def test_sleep_mode_enabled(self):
         utils._SLEEP_MODE_ENABLED = None