Add tests on Windows with python 3.8

.gitlab-ci.yml

@@ -59,6 +59,12 @@ windows_test_python37:
   dependencies:
     - windows_wheel_python3
 
+windows_test_python38:
+  <<: *test_template_defintion
+  extends: .windows_base_python38
+  dependencies:
+    - windows_wheel_python3
+
 
 macos_test_python36:
   <<: *test_template_defintion