Remove unneeded list when defining single cpu pytest mark

Co-authored-by: Matthew Roeschke <[email protected]>

Author: datapythonista

pandas/tests/io/test_iceberg.py

@@ -16,7 +16,7 @@
 
 from pandas.io.iceberg import read_iceberg
 
-pytestmark = [pytest.mark.single_cpu]
+pytestmark = pytest.mark.single_cpu
 
 pyiceberg = pytest.importorskip("pyiceberg")
 pyiceberg_catalog = pytest.importorskip("pyiceberg.catalog")