%run magic does not use __main__.py when called on module path

[astromancer]

Here's a small demo package:

test_main/
├── __init__.py
└── __main__.py

With __init__.py having one line of code:

print('ran __init__.py')

and __main__.py:

print('ran __main__.py')
variable = 1

Here are a few example that show how this fails:
In [1]: !ls test_main/
__init__.py __main__.py

In [2]: import test_main
ran __init__.py

In [3]: %run test_main
ERROR:root:File 'test_main.py' not found.

Using the -m switch seems to work however, the one does not get access to the module namespace like you would when running a regular script. I.e the variable above remains undefined, which is undesirable for interactive work.
In [4]: %run -m test_main
ran __main__.py

In [4]: variable

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-5-1748287bc46a> in <module>
----> 1 variable

NameError: name 'variable' is not defined

To get access to the namespace one has to provide the full path.
%run test_main/__main__.py
ran __main__.py
In [9]: variable
Out[9]: 1

Wondering if it would be possible to get the __main__.py script to run when calling the %run on the module path?

[astromancer]

related to #9812