Update Cabal to BinaryLiterals-aware 1.20 version

In 1c0b5fdc9f2b6ea8166cc565383d4cd20432343c (re #9224) `BinaryLiterals`
was temporarily added to T4437's `expectedGhcOnlyExtensions` list. This
can now reverted as Cabal has been made aware of `BinaryLiterals`
(see haskell/cabal#1970 and haskell/cabal#1972).

updates Cabal submodule

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>