[CI] Test with Python 3.12

[PrimozGodec]

Description of changes

• Test Orange on Python 3.12, which has been out for some time now.
• Replace distutils, which was deprecated and removed in Python 3.12 form tests.
• Replace wrongly used called_with (should be assert_called_with) in test_owpredictions. Since it was not even a valid check (selection model change when the model is set to None in the widget), I replaced it with just assert_called_once, which checks that unregister was called.

Includes

• Code changes
• Tests
• Documentation

[PrimozGodec]

I think the issue should be solved when Catboost provides Python 3.12 wheels. I asked them if they could provide them.

[codecov]

Codecov Report

Merging #6729 (e03201c) into master (f970414) will increase coverage by 0.00%.
Report is 8 commits behind head on master.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6729   +/-   ##
=======================================
  Coverage   88.15%   88.15%           
=======================================
  Files         323      323           
  Lines       70749    70748    -1     
=======================================
+ Hits        62369    62371    +2     
+ Misses       8380     8377    -3     

[PrimozGodec]

Waiting for pavlin-policar/openTSNE#255

[ales-erjavec]

Why this downgrade?

[PrimozGodec]

Thanks for checking. It probably remained the same from the previous version of PR. Fixed now.