Temporarily skip macro tests on Windows

We re-use the swift-syntax libs from the real build to avoid re-building
it in these tests, but it currently only handles the SwiftPM build and
not Windows.

Temporarily continue skipping these on Windows to unblock CI.

Author: bnbarham

Sources/SKTestSupport/SkipUnless.swift

@@ -140,6 +140,12 @@ package actor SkipUnless {
     file: StaticString = #filePath,
     line: UInt = #line
   ) async throws {
+    #if os(Windows)
+    try SkipUnless.platformIsWindows(
+      "Temporarily skipping as we need to fix these tests to use the cmake-built swift-syntax libraries on Windows."
+    )
+    #endif
+
     return try await shared.skipUnlessSupported(file: file, line: line) {
       do {
         let project = try await SwiftPMTestProject(