We don't backport PRs merged into doc/releases. Therefore, when one browses to an older Ceph release version on docs.ceph.com (e.g., https://docs.ceph.com/en/pacific/), the information is out of date at best.
The doc/releases page is only accurate if browsing https://docs.ceph.com/en/latest/, for example.
So this post_checkout command will make sure we've checked out doc/releases from main before building and publishing.
Signed-off-by: David Galloway <dgallowa@redhat.com>