Build fix: TestBundle

Ensure TestBundle imports using `@testable import`.

Author: millenomi

TestFoundation/TestBundle.swift

@@ -9,6 +9,14 @@
 
 import CoreFoundation
 
+#if NS_FOUNDATION_ALLOWS_TESTABLE_IMPORT
+    #if canImport(SwiftFoundation) && !DEPLOYMENT_RUNTIME_OBJC
+        @testable import SwiftFoundation
+    #else
+        @testable import Foundation
+    #endif
+#endif
+
 internal func testBundle() -> Bundle {
     #if DARWIN_COMPATIBILITY_TESTS
     for bundle in Bundle.allBundles {