Fix subsref on Octave >= 9: pycall: no such Python function or callable: getattr

Perhaps the subsref has changed a bit:

py.math.sqrt is now calling subsref.m from pyobject on py.math. AFAICT, it didn't before.

py.math is a module. And has no getattr.

TODO: figure out what this does on Octave 8.4.0:

A = py.math
class(A)
A.sqrt
A.sqrt(2)