Add missing test decorator for test_util_inspect (#11321)

Author: marxin

tests/test_util_inspect.py

@@ -670,6 +670,7 @@ def __get__(self, obj, typ=None):
         pass
 
 
+@pytest.mark.sphinx(testroot='ext-autodoc')
 def test_isproperty(app):
     from target.functions import func
     from target.methods import Base