bug#36700: 27.0.50; python-mode beginning-of-defun broken

[Yilin Wei]

Hi,

The function `beginning-of-defun` seems to be be broken if
there is a nested class definition in the function.

I think this also means that `(thing-at-point 'defun)` isn't working
as expected.

Behaviour:

def moo():
    class Test:
      pass
    <-
   
When the cursor is at the location marked, running (beginning-of-defun)
makes the cursor go to the wrong location, shown below, instead of to
the beginning of the def.

def moo():
<-   class Test:
       pass

Yilin