tests: Add a PipelineRun ServiceAccounts test 🍊
tests: Add a PipelineRun ServiceAccounts test 🍊

This adds a test to validate the ServiceAccountName,
ServiceAccountNames and TaskRunSpec.ServiceAccountName are all working
as expected.

Signed-off-by: Vincent Demeester <b98c0fd48a8945096c766de790fe70420dd2f223@redhat.com>

tektoncd/pipeline,tektoncd/pipeline