CI: Enable mswin version of Ruby

Author: mrkn

.github/workflows/windows.yml

@@ -27,9 +27,9 @@ jobs:
         - 2.x
         python_architecture:
         - x64
-        #include:
+        include:
+        - { os: windows-latest , ruby: mingw , python: 3.x , python_architecture: x64 }
         #- { os: windows-latest , ruby: mswin , python: 3.x , python_architecture: x64 }
-        #- { os: windows-latest , ruby: mingw , python: 3.x , python_architecture: x64 }
 
     steps:
     - uses: actions/checkout@v2