Add ghcup 0.1.19.5 prerelease

[hasufell]

@hsyl20

[hasufell]

Bindist test: https://github.com/haskell/ghcup-metadata/actions/runs/5530130931

[hasufell]

GHCup with cross support can be tested following: https://www.haskell.org/ghcup/guide/#pre-release-channels

E.g. after an emscripten installation:

ghcup config add-release-channel https://raw.githubusercontent.com/haskell/ghcup-metadata/develop/ghcup-prereleases-0.0.7.yaml
ghcup upgrade
ghcup config add-release-channel https://raw.githubusercontent.com/haskell/ghcup-metadata/develop/ghcup-cross-0.0.8.yaml
emconfigure ghcup install ghc --set javascript-unknown-ghcjs-9.6.2

Resulting ghc binary will be called javascript-unknown-ghcjs-ghc.

Maybe will need to write a blog post or discourse post. Will also build more bindists manually... currently only linux: https://downloads.haskell.org/~ghcup/unofficial-bindists/ghc/javascript-unknown-ghcjs-9.6.2/