Explain the Swift versions list for Windows

Author: glessard

.github/workflows/swift_package_test.yml

@@ -34,7 +34,8 @@ on:
       windows_swift_versions:
         type: string
         description: "Include Windows Swift version list (JSON)"
-        default: "[\"5.9\", \"5.10\", \"6.0\", \"6.1\", \"nightly\", \"nightly-6.2\"]"
+        # "5.10" is omitted for Windows because the container image is broken.
+        default: "[\"5.9\", \"6.0\", \"6.1\", \"nightly\", \"nightly-6.2\"]"
       windows_exclude_swift_versions:
         type: string
         description: "Exclude Windows Swift version list (JSON)"