Add OverloadedRecordUpdate to KnownExtension

Cabal-syntax/src/Language/Haskell/Extension.hs

@@ -861,6 +861,11 @@ data KnownExtension =
   -- | Enable the use of record dot-accessor and updater syntax
   | OverloadedRecordDot
 
+  -- | Provides record @.@ syntax in record updates, e.g. @x {foo.bar = 1}@.
+  --
+  -- * <https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/exts/overloaded_record_update.html#extension-OverloadedRecordUpdate>
+  | OverloadedRecordUpdate
+
   -- | Enable data types for which an unlifted or levity-polymorphic result kind is inferred.
   | UnliftedDatatypes