ci: serialize pool trim test for known driver synchronization issue

Refs: #3350. Preserve every parameter and assertion; only concurrent execution is disabled for this affected test.
Signed-off-by: Ralf W. Grosse-Kunstleve <rgrossekunst@nvidia.com>

Author: rwgk

cuda_core/tests/test_memory.py

@@ -2946,6 +2946,7 @@ def test_mempool_watermark_reset(memory_resource_factory, kind):
         mr.close()
 
 
+@pytest.mark.thread_unsafe(reason="CUDA driver synchronization crash with concurrent pool cleanup; see gh-3350")
 @pytest.mark.agent_authored(model="claude-opus-5-5")
 def test_mempool_trim(memory_resource_factory):
     device = Device()