At some point the upstream changed and gitstatus.prompt.zsh stopped
working. The issue was that this file expects to be able to run the
"install" script in the same directory.
- Install the "install" script and "build.info" file that
gitstatus.prompt.zsh expects to be able to find when it runs.
- Patch the install script so that it defaults to not automatically
installing gitstatus. This can still be overridden by setting
GITSTATUS_AUTO_INSTALL=1, although I'm not sure why anyone would do
this if they've already installed gitstatus with Nix.
- Add an install check phase that tests the zsh integration to prevent
this derivation from breaking in the same way in the future. (This
also ends up testing the binary itself.)
Fixes#96135.
c278c6fd55