test(cuda.core): gate register() IPC guard test on mempool support

test_register_rejects_non_ipc_memory_resource constructed a
DeviceMemoryResource from a bare Device(), which raises
CUDA_ERROR_NOT_SUPPORTED on devices without memory pool support. Every
win-64 TCC job in CI failed there before reaching the assertion under
test.

Take the mempool_device fixture instead, matching how the other
mempool-dependent tests are gated. The fixture skips when
memory_pools_supported is false and already makes the device current,
so the manual Device()/set_current() pair is dropped.

Author: fedonman

cuda_core/tests/memory_ipc/test_errors.py

@@ -53,11 +53,9 @@ def test_ipc_allocation_handle_rejects_negative_fd():
 
 
 @pytest.mark.human_authored
-def test_register_rejects_non_ipc_memory_resource():
+def test_register_rejects_non_ipc_memory_resource(mempool_device):
     """register() on a resource without IPC enabled raises instead of dereferencing None."""
-    device = Device()
-    device.set_current()
-    mr = DeviceMemoryResource(device)
+    mr = DeviceMemoryResource(mempool_device)
     assert not mr.is_ipc_enabled
 
     key = uuid.uuid4()