Workflow jobs does not have the BranchJobProperty set but
multibranchproject has it. The previous code filtered all workflow jobs
not having this property making the plugin GitHub Authorization Settings
not working for those workflow jobs (all simple pipelines).

So in order to make multibranch build cancellable we also need to take
those jobs into account. Those jobs don't have SCMs setup so we need to
get the scm from the BranchJobProperty like it was done before.

So, now we check if the BranchJobProperty is set and do the adequate
commands to get the scm.

Also, added tests for CANCEL permission which was never tested.