[Bugfix] Restore torch default device between tests (#8157)

Signed-off-by: wangyu <410167048@qq.com>

tests/diffusion/conftest.py

@@ -1,15 +0,0 @@
-# SPDX-License-Identifier: Apache-2.0
-# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
-
-import pytest
-import torch
-
-
-@pytest.fixture(autouse=True)
-def restore_torch_default_dtype():
-    """Keep process-global dtype changes from leaking between diffusion tests."""
-    default_dtype = torch.get_default_dtype()
-    try:
-        yield
-    finally:
-        torch.set_default_dtype(default_dtype)