vscode-haskell needs direct access to ghcup to run its test successfully. Until recently, ghcup was always on $PATH and we could simply run ghcup install ... and install all the binaries that we needed. Additionally, the tests themselves also call ghcup install.

However, this seems to have changed recently for macos-latest: https://github.com/haskell/vscode-haskell/actions/runs/9015398738/job/24769933756?pr=1077

It looks like ghcup is not on the $PATH any more, but hidden somewhere in the hostedtoolcache.

One way to work around this for good, is to provide the path to ghcup as an action output, then we don't have to rely on ghcup to be on the $PATH, and can find it reliably.