test: mark PR basnijholt#1379 regression test as xfail

The test documents an unfixed bug (proactive adaptation context not
cleared on light.turn_off, causing second split command to be sent
to an off light). Upstream basnijholt#1379 added the test without the fix, so
we xfail it until the bug is addressed.

Author: Florian Horner

tests/test_switch.py

@@ -2995,6 +2995,10 @@ async def _flush_attr_state(hass, entity_id):
     ), f"AL overrode manual brightness {manual_brightness} with {al_brightness}"
 
 
+@pytest.mark.xfail(
+    reason="Regression test from upstream PR #1379 — underlying bug not yet fixed",
+    strict=False,
+)
 async def test_separate_turn_on_commands_respects_light_off_state(hass):
     """Test that split commands are not sent when light is turned off between commands.