Split out unit tests from CI matrix
Split out unit tests from CI matrix

refs https://github.com/TryGhost/Toolbox/issues/208

- unit tests (shouldn't) be database dependent so they don't need to be
  included in the DB matrix
- this prevents an extra 6 executions of unit tests, which isn't a big
  deal given they only take 10s to run, but semantically they belong
  outside so this commit does that
- also updates the canary step to rely on this extra test run

e10/Ghost,e10/Ghost,TryGhost/Ghost,TryGhost/Ghost,TryGhost/Ghost