Fix "Failed to get a function signature" sphinx warnings.

I found the fix here: https://github.com/dask/dask/pull/11035/files

hoomd/custom/custom_operation.py

@@ -132,8 +132,12 @@ def __init__(cls, name, base, dct):  # noqa: N805
             return
         extra_methods = dct.get("_wrap_methods", [])
         for name in itertools.chain(action_cls._export_dict, extra_methods):
+            method = getattr(action_cls, name)
+            if isinstance(method, property):
+                method = method.fget
+
             wrapped_method = _AbstractLoggableWithPassthrough._wrap_loggable(
-                name, getattr(action_cls, name))
+                name, method)
             setattr(cls, name, wrapped_method)
         cls._export_dict = action_cls._export_dict
         _AbstractLoggable.__init__(cls, name, base, dct)