Move package-and-qa to the test phase

The problem is this: when each phase starts, it checks if all jobs in earlier phases are complete. package-and-qa is slow. As build is the first phase, if you trigger package-and-qa before the prepare phase is finished, the entire test phase will be blocked until package-and-qa completes, which isn't what we want.

But equally, if build came after test, then package-and-qa couldn't be started until the tests were finished. Putting it in the same stage as the tests means we can have our cake and eat it.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/50718.