Ensure tmp/tests exists before extracting the Workhorse package

In the case where the Gitaly binaries cache isn't downloaded, tmp/tests wouldn't exist, and extract_gitlab_workhorse_package would fail to extract the Workhorse archive to tmp/tests. See an example at https://gitlab.com/gitlab-org/gitlab/-/jobs/2268357221#L70.

This MR ensures that the folder exists prior to extracting the archive to it.