ref: #29

if GH_HOST is set to anything other than github.com, gh grep cannot be executed. Because it cannot retrieve the tag, as it is now set to retrieve the tag using gh-cli.

Specifically, the tag becomes an empty string, and the string for the exe becomes like gh-grep__linux_amd64. It can be reproduced with the following command.

GH_HOST=<your-github.example.com> gh grep help