Don't update site on branches, but still see the results?

Currently, cmucl-site generates the site on any branch.  This also means
that any in-progress branch modifies the official site.  I think this
should only happen for the main branch (or some other official branch).
For other branches, I want it uploaded so I can see the results, but
doesn't update the official site.

Any ideas on this?  Will staging areas work?  What about gitlab
environments?

-- 
Ray