tests: fix PYTHONPATH manipulation on Windows Without the semicolon separator and quotes, the variables ends up like this: c:\Users\Matt\projects\hg-evolve:c:\Users\Matt\projects\hg-evolve: c:\Users\Matt\projects\hg;c:\Users\Matt\projects\hg-evolve\tests; c:\Users\Matt\projects\hg\tests That in turn makes the local evolve code unreachable, and the system installed code is tested instead. I'm testing against `uname` instead of a trivial python script printing os.name because maybe one day tests will run on WSL.