Fixing OMPython at v3.6

[AnHeuermann]

Issue

Related to #243.

Changes

• Fixing OMPyton at version 3.6.
  • Newer OMPython 4.0.0 introduces breaking changes.
• Changing MSYS environment to UCRT64 for Windows tests. No idea how this could work for so long.

[AnHeuermann]

The error message from OpenModelica v1.25.5 on Windows:

[Timeout remaining time 658]
"C:/Program Files/OpenModelica1.25.5-64bit\share\omc\scripts\Compile.bat" MyLibrary_1.0.0_MyLibrary.Blocks.Examples.PID_Controller gcc mingw64 parallel dynamic 24 0 [Timeout 660]
"C:/Program Files/OpenModelica1.25.5-64bit\share\omc\scripts\Compile.bat" MyLibrary_1.0.0_MyLibrary.Blocks.Examples.PID_Controller gcc mingw64 parallel dynamic 24 0 The system cannot find the path specified.

PATH = "D:\a\OpenModelicaLibraryTesting\OpenModelicaLibraryTesting\MyLibrary_1.0.0_MyLibrary.Blocks.Examples.PID_Controller;D:\a\OpenModelicaLibraryTesting\OpenModelicaLibraryTesting\MyLibrary_1.0.0_MyLibrary.Blocks.Examples.PID_Controller\..\..\usr\bin;"

The system cannot find the path specified.

[Calling os._exit(0), Time elapsed: 5.5470000000000255]
Failed to read output from testmodel.py, exit status != 0:
1.4380000000001019 1.4622137 1.0325389
Calling exit ...
<OMPython.OMCSessionZMQ object at 0x00000287B0649000>

OpenModelica should ship with MSYS UCRT64, not MINGW64. But than why does the nightly succeed?
Let's try to change the CI to use ucrt64 on Windows.