Update GitHub CI for Windows

Author: colemancda

.github/workflows/swift-windows.yml

@@ -0,0 +1,13 @@
+name: Swift Windows
+on: [push]
+jobs:
+  windows-build:
+    runs-on: windows-latest
+    steps:
+      - uses: compnerd/gha-setup-swift@main
+        with:
+          branch: swift-6.1-release
+          tag: 6.1-RELEASE
+      - uses: actions/checkout@v2
+      - run: swift build
+      - run: swift test