CMake/multipy: bornagain.deg not found

Bug introduced by multipy:

Under Linux, built and installed current main. Running a Python script from the command line:

$ python3 /io/CylindersAndPrisms.py
Traceback (most recent call last):
  File "/io/CylindersAndPrisms.py", line 6, in <module>
    from bornagain import deg, nm
ImportError: cannot import name 'deg' from 'bornagain' (unknown location)

Or interactively:

$ python3
Python 3.9.10 (main, Jan 16 2022, 17:12:18) 
[GCC 11.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import bornagain as ba
>>> ba.deg
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'bornagain' has no attribute 'deg'
>>> from bornagain import deg
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: cannot import name 'deg' from 'bornagain' (unknown location)

I suppose this problem has been introduced by the multi-python changes.