[cmake] Add missing locale_notifications.swift (#885)

Author: etcwilde

Sources/FoundationEssentials/Locale/CMakeLists.txt

@@ -18,6 +18,7 @@ target_sources(FoundationEssentials PRIVATE
     Locale.swift
     Locale_Autoupdating.swift
     Locale_Cache.swift
+    Locale_Notifications.swift
     Locale_Preferences.swift
     Locale_Protocol.swift
     Locale_Unlocalized.swift)