CI: run on windows

Don't know if it works, let's try :-)

Author: cben

.github/workflows/actions.yml

@@ -16,7 +16,9 @@ jobs:
       matrix:
         ruby: [ '2.5', '2.6', '2.7', '3.0', '3.1', 'ruby-head', 'truffleruby-head' ]
         os_and_command:
-        - os: 'macos-latest'
+        - os: macos-latest
+          command: 'env TESTOPTS="--verbose" bundle exec rake test'
+        - os: windows-latest
           command: 'env TESTOPTS="--verbose" bundle exec rake test'
         - os: ubuntu-latest
           # Sometimes minitest starts and then just hangs printing nothing.