WireGuardKit: Set publicHeadersPath = "." to flatten public headers structure

Signed-off-by: Andrej Mihajlov <and@mullvad.net>

Sources/WireGuardKitC/module.modulemap

@@ -1,4 +1,4 @@
 module WireGuardKitC {
-    umbrella header "include/WireGuardKitCTarget.h"
+    umbrella header "WireGuardKitC.h"
     export *
 }