except it is probably not set in this env for some dumb reason

Previous CI runs created TARGET_BRANCH and updated it but failed to push.  But
the branch still exists in the CI environment, with the changes!  Hooray.
Mutable shit!

I don't think this is really the fix but it _is_ shell, we don't need those
parents, let's see.

This makes it easier to test outside of GitLab and it also means we don't
depend on whatever wacko shell settings we inherit from GitLab.

This avoids a prompt at deploy time and the possibility of an MitM attack
against TOFU.