Integrate stylish-haskell into hls executable with ghc 9.8

[jhrcek]

The version of stylish-haskell where @michaelpj added support for ghc 9.8 is on hackage:
https://hackage.haskell.org/package/stylish-haskell-0.14.6.0/changelog
Let's enable it in hls!

[jhrcek]

Bumping index state just to silence this warning:

Warning: Requested index-state 2024-02-25T00:00:00Z is newer than 
'hackage.haskell.org'! Falling back to older state (2024-02-24T17:42:44Z).

[fendor]

I am a little bit confused, why didn't CI report the command cabal test hls-stylish-haskell plugin as failing? https://github.com/haskell/haskell-language-server/blob/master/.github/workflows/test.yml#L170

[jhrcek]

Hmm, good question.
What motivated me to open this PR was that I was playing with ghc 9.8 and formatting hs files (with stylish-haskell selected as formatter in hls options) didn't do anything. So I thought "maybe stylish-haskell is not yet enabled". So I looked at hls cabal file and saw if impl(ghc < 9.8.0) and just removed it.
After closer look I see that this conditional is part of common stylishHaskell stanza which is not used anywhere EDIT: used in the haskell-language-server library section to disable integrating stylish plugin into hls executable.

But the plugin itself and its tests were NOT marked as buildable: False that's why you can see its tests running on master. It was just not integrated into hls executable.

[michaelpj]

Oops, I thought I had done this 🤦