test(capi): mark the folded-UDF close() scenario as a known C-API failure

The C-API backend cannot register UDFs yet, so close_from_a_folded_udf stops at
create_function() with NotImplementedError, like close_from_a_udf already listed
here. The C-API job never reached pytest on this branch before, because its JSON
extension smoke step crashed on the ladybug main build of the time.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: 2 people

test/capi_xfails.py

@@ -81,6 +81,7 @@
         "test/test_udf.py::test_udf_null",
         "test/test_udf.py::test_udf_except",
         "test/test_udf.py::test_udf_remove",
+        "test/test_connection_close.py::test_close_with_query_in_flight[close_from_a_folded_udf]",
         "test/test_connection_close.py::test_close_with_query_in_flight[close_from_a_udf]",
         "test/test_udf_reentrancy.py::test_udf_calling_a_connection[idle_other_connection]",
         "test/test_udf_reentrancy.py::test_udf_calling_a_connection[same_connection_on_a_worker]",