Included `v4.*` branches in CI testing
Included `v4.*` branches in CI testing

no issue

- as we're making more and more use of branches for releases, we want
  tests to run on them
- this commit adds the v4 wildcard to the GitHub workflow so it'll
  trigger when we push to them

ErisDS/Ghost,e10/Ghost,e10/Ghost,TryGhost/Ghost,janvt/Ghost,ErisDS/Ghost,janvt/Ghost,ErisDS/Ghost,TryGhost/Ghost,TryGhost/Ghost