Set branch-protection-tighten as manual

The job branch-protection-tighten is triggered with the same rules as
branch-protection-relax, which is confusing. Instead of making it to
depend on the stage, keep it independent of it thanks to "needs" but
set it to be manual. In this way the user  can to check that everything
is OK and also to allows him to run this job at any stage even if some
of the branching job had failures.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>