Fix python docstring auto-fill (Bug#36056)

Fix python docstring auto-fill (Bug#36056)

* lisp/progmodes/python.el (python-mode): Set
fill-indent-according-to-mode locally to t.  This lets auto-fill do
the right thing when auto-filling inside a docstring.  The default was
to nil on 2001-11-25 "(fill-indent-according-to-mode): Default to nil"
with the comment that it "screws up CC-mode's filling tricks".  But
presumably it shouldn't be a problem for python-mode.
* test/lisp/progmodes/python-tests.el (python-auto-fill-docstring):
New test.