Repository archive URL seems to have changed, leading to wrong tarballs being generated

Initially reported by sangy on IRC (@sangy ?)

In previous releases, this URL:

https://gitlab.com/gitlab-org/gitlab-pages/repository/archive.tar.gz?ref=v0.7.0

would return a tarball for the tagged release.

With v10.7.0rc6, it instead returns a tarball for master.

The tags UI now points people at URLs of this form instead:

https://gitlab.com/gitlab-org/gitlab-pages/-/archive/v0.7.0/gitlab-pages-v0.7.0.tar.gz

I know that we don't guarantee stable URLs outside of the API, but this strikes me as a bug because a previously-working URL is now serving the wrong content, rather than serving a 404 error. This is unexpected and sure to break a range of deployment and release automations in unexpected and hard-to-detect ways.

I recall we picked something relating to archives into v10.7.0rc6 - perhaps this is related? I'll do some digging.