test(multiple): fix failing tests

[wpbonelli]

Fix tests whose failures were suppressed before #2335:

• skip snapshot on mac for test_mp7.py::test_mp7_output, mp7 results differ slightly for some reason
• fix the venv bin/lib directory names on Windows in test_generate_classes.py

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.2%. Comparing base (5555d15) to head (f270662).
Report is 10 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #2338     +/-   ##
=========================================
- Coverage     74.3%   74.2%   -0.2%     
=========================================
  Files          294     294             
  Lines        59562   59749    +187     
=========================================
+ Hits         44282   44360     +78     
- Misses       15280   15389    +109     

see 17 files with indirect coverage changes