Fix Portainer tests hanging on real event listener (#180464)

tests/components/portainer/conftest.py

@@ -139,9 +139,13 @@ def mock_portainer_client(mock_portainer_watcher: MagicMock) -> Generator[AsyncM
         yield client
 
 
-@pytest.fixture
+@pytest.fixture(autouse=True)
 def mock_portainer_event_listeners() -> Generator[dict[int, MagicMock]]:
-    """Mock PortainerEventListener; one MagicMock instance per endpoint_id."""
+    """Mock PortainerEventListener; one MagicMock instance per endpoint_id.
+
+    Autouse because the real listener reconnects in a tight loop when its
+    event stream ends immediately, as the mocked client's does.
+    """
     instances: dict[int, MagicMock] = {}
 
     def _factory(