chore(cabal): update haskell language edition to GHC2021

This includes a good set of default language extensions that are
often used by us. It frees us of explicitly importing common extensions.

Ref: https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/control.html#extension-GHC2021

Signed-off-by: Taimoor Zaeem <taimoorzaeem@gmail.com>

src/library/PostgREST/App.hs

@@ -9,12 +9,10 @@ Some of its functionality includes:
 - Producing HTTP Headers according to RFCs.
 - Content Negotiation
 -}
-{-# LANGUAGE FlexibleContexts    #-}
-{-# LANGUAGE LambdaCase          #-}
-{-# LANGUAGE NamedFieldPuns      #-}
-{-# LANGUAGE RecordWildCards     #-}
-{-# LANGUAGE ScopedTypeVariables #-}
-{-# LANGUAGE ViewPatterns        #-}
+{-# LANGUAGE LambdaCase      #-}
+{-# LANGUAGE NamedFieldPuns  #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE ViewPatterns    #-}
 module PostgREST.App
   ( postgrest
   , run