X.Config: Appease -Werror=type-equality-requires-operators

GHC 9.4 complains:

    The use of ‘~’ without TypeOperators
    will become an error in a future GHC release.

src/XMonad/Config.hs

@@ -1,5 +1,6 @@
 {-# OPTIONS_GHC -fno-warn-missing-signatures -fno-warn-orphans #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  XMonad.Config