Update cabal-version to 3.14

[Aster89]

Attempt at updating cabal-version to 3.14.

The real motivation is to have the extra-files stanza in which to move most files currently listed under extra-source-files; doing so would improve the developer experience by preventing cabal run/build from rebuilding the project when only */testdata/* files are changed.

[fendor]

Looks like stackage lts23 doesn't support building with Cabal-3.14.

The lts23 is quite old, so I think we can argue that we should upgrade the snapshot. We can probably drop that lts version or upgrade it to https://www.stackage.org/lts-23.28, to bump to GHC 9.8. GHC 9.6 will be dropped after the next release, so I think it is fine to not test it in CI with stack any more.

The failures with cabal are caused by old ormolu versions. I don't think we can simply force a newer ormolu version. In https://github.com/haskell/haskell-language-server/blob/master/haskell-language-server.cabal#L1454C1-L1454C63, we see

    , ormolu          ^>=0.5.3 || ^>= 0.6 || ^>= 0.7 || ^>=0.8

I doubt we actually support ^>=0.5.3 || ^>= 0.6 but https://hackage.haskell.org/package/ormolu-0.7.7.0 only works with Cabal-syntax (>=3.12 && <3.13), and ghc-lib-parser (>=9.10 && <9.11). So that sounds like an issue.
To be sure, I am unsure, but it looks like the GHC 9.10 CI might have succeeded, so maybe there is some more wiggle room.

TL;DR, this PR can't be merged right away until we manage to upgrade the ormolu version to 0.8 which only works for GHC >=9.12.