ignore the deprecation warning in the constructor validation test

Author: MBrouns

pandas/tests/window/test_expanding.py

@@ -16,6 +16,9 @@ def test_doc_string():
     df.expanding(2).sum()
 
 
+@pytest.mark.filterwarnings(
+    "ignore:The `center` argument on `expanding` will be removed in the future"
+)
 def test_constructor(which):
     # GH 12669