Gitlab::Git::Hook should set the GL_REPOSITORY environment variable

https://sentry.gitlap.com/gitlab/devgitlaborg/issues/34971/events/2130800/

When introducing the GL_REPOSITORY variable we overlooked the Gitlab::Git::Hook class.

This has been causing PostReceive jobs to fail on dev.gitlab.org since https://gitlab.com/gitlab-org/gitlab-shell/merge_requests/136 was merged.

The GL_REPOSITORY variable should be among those set on the hook process.