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/distributed/conftest.py

@@ -1,7 +1,6 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 import random
-from typing import Optional, Union
 
 import msgspec
 import msgspec.msgpack
@@ -78,8 +77,8 @@ class MockSubscriber:
 
     def __init__(
         self,
-        pub_endpoints: Union[str, list[str]],
-        replay_endpoints: Optional[Union[str, list[str]]] = None,
+        pub_endpoints: str | list[str],
+        replay_endpoints: str | list[str] | None = None,
         topic: str = "",
         decode_type=SampleBatch,
     ):
@@ -111,7 +110,7 @@ class MockSubscriber:
         self.last_seq = -1
         self.decoder = msgspec.msgpack.Decoder(type=decode_type)
 
-    def receive_one(self, timeout=1000) -> Union[tuple[int, SampleBatch], None]:
+    def receive_one(self, timeout=1000) -> tuple[int, SampleBatch] | None:
         """Receive a single message with timeout"""
         if not self.sub.poll(timeout):
             return None