When I try to run the install script as in the readme it insists on downloading ghc-8.6.5
$ stack ./install.hs hls-8.8.4
ghc-8.6.5: 8.61 MiB / 175.83 MiB ( 4.90%) downloaded...^C
The install script is run with ghc 8.6.5.
So, this is expected behaviour.
To match the ghc used by the script and the used one for install hls, you can change the resolver of ./install/shake.yaml to match the stack-${ghcVersion}.yaml one
I think we can close this then, but just to clarify for anyone else stumbling across this ghc-8.6.5 is the version of ghc being downloaded to run the installer script itself, not for haskell-language-server