add ability to install pythonnet using git+https

.appveyor.yml

@@ -11,14 +11,20 @@ environment:
     - PYTHON: C:\Python38
     - PYTHON: C:\Python38-x64
     - PYTHON: C:\Python39
+      CLONE_PYTHONNET: "true"
     - PYTHON: C:\Python39-x64
+      CLONE_PYTHONNET: "true"
 
 install:
   - set PATH=%PYTHON%;%PYTHON%\Scripts;%PATH%
   - python --version
   - python -m pip install --upgrade pip
   - python -m pip install --upgrade setuptools wheel
   - python -m pip install --upgrade PySide2 pytest pytest-cov pytest-runner
+  - IF "%CLONE_PYTHONNET%"=="true" (
+      python -m pip install pycparser &&
+      python -m pip install git+https://github.com/pythonnet/pythonnet.git &&
+    )
   - python -m pip list
   - python -c "from PySide2.QtWidgets import QApplication; QApplication([])"
 

setup.py

@@ -135,7 +135,7 @@ def get_version():
 install_requires = []
 
 tests_require = ['pytest', 'pytest-cov', 'PySide2']
-if sys.platform == 'win32':
+if sys.platform == 'win32' and sys.version_info[:2] < (3, 9):
     tests_require.append('pythonnet')
 
 testing = {'test', 'tests', 'pytest'}.intersection(sys.argv)