Enable Ruby 3.0 CI on windows

Author: kenhys

.github/workflows/windows.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [ '2.5', '2.6', '2.7' ]
+        ruby: [ '2.5', '2.6', '2.7', '3.0' ]
         os:
           - windows-latest
     name: Ruby ${{ matrix.ruby }} unit testing on ${{ matrix.os }}