[AMD] [CI] Fix tests for v0.28.0 (#6830)

Signed-off-by: tjtanaa <tunjian.tan@embeddedllm.com>

tests/diffusion/conftest.py

@@ -0,0 +1,15 @@
+# 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)