do not run 4 on win

Author: KazuCocoa

.github/workflows/unittest.yml

@@ -39,7 +39,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [3.1, 3.2, 3.3, 4.0]
+        # 4.0 is not available on Win env yet.
+        ruby: [3.1, 3.2, 3.3]
 
     runs-on: windows-latest