support ghc-9.14

self-bootstrapping ghc-9.14  (and possibly also any other use of hashable with ghc-9.14) "will require a bounds bump in hashable", cf. resolution of https://gitlab.haskell.org/ghc/ghc/-/issues/26342 

The linked ticket didn't make it clear whether the issue was reported upstream. It is not critical for me (I can use `--allow-newer` in my projects).