Import Foundation to make Xcode 14.3 happy (pointfreeco#97)

Author: amonshiz

Sources/_SwiftUINavigationState/Internal/RuntimeWarnings.swift

@@ -37,6 +37,7 @@ public func runtimeWarn(
 
   #if canImport(os)
     import os
+    import Foundation
 
     // NB: Xcode runtime warnings offer a much better experience than traditional assertions and
     //     breakpoints, but Apple provides no means of creating custom runtime warnings ourselves.