CI: Migrate CI for Windows from AppVeyor to GitHub Actions

Signed-off-by: Takuro Ashie <[email protected]>

Author: ashie

.github/workflows/unit-test.yml

@@ -11,7 +11,11 @@ jobs:
       fail-fast: false
       matrix:
         ruby: [ '3.2', '3.1', '3.0', '2.7' ]
-        os: [ 'ubuntu-latest', 'macOS-latest' ]
+        os: [ 'ubuntu-latest', 'macOS-latest', 'windows-latest' ]
+        # It should be removed after RubyInstaller 3.2 is available on setup-ruby
+        exclude:
+          - os: windows-latest
+            ruby: 3.2
     name: Ruby ${{ matrix.ruby }} unit testing on ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v2