Bug 1751515 - Part 3: Do not install artifact test archive when `--disable-tests`. r=firefox-build-system-reviewers,glandium

When consuming artifacts from `Bs` jobs, there is no test archive.
The consumer still needs to specify "no tests", but this at least
allows the artifact build to proceed.

Differential Revision: https://phabricator.services.mozilla.com/D136930