wheel: assign CIBW_SKIP globally The other cibuildwheels (e.g. windows) will needs it too.

windows: simply rely on the PATH adjustment to find python.exe in tests The shell script under a `.exe` name confused Windows outside MSYS and give us the following error: […]/python.exe is not compatible with the version of Windows you're running. Check your computer's system information and then contact the software publisher. This is necessary to get the wheel variant of the test run to work properly.

ci: adjust port range on windows too This will help having concurrency on the windows runner too.