Update Optional[x] -> x | None and Union[x, y] to x | y (#26633)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

tests/v1/entrypoints/llm/test_struct_output_generate.py

@@ -2,8 +2,6 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
-from __future__ import annotations
-
 import json
 from dataclasses import fields
 from enum import Enum
@@ -30,6 +28,8 @@ from vllm.sampling_params import (
 
 if TYPE_CHECKING:
     from vllm.config.model import TokenizerMode
+else:
+    TokenizerMode = str
 
 NGRAM_SPEC_CONFIG = {
     "model": "[ngram]",