test_result: add Reference property sheet on Test Suite Repository

This property sheet was missing, but test passed because both the
setSourceReference and getSourceReference were acquired. Change also the
test to use edit(source_reference=) which is what happens when editing
in the UI.
3 jobs for <span class="ref-name">fix/test_suite_repo_accessor</span> in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-TestRunner1

00:44:40

failed ERP5.PerformanceTest-TestRunner1

00:32:12

failed ERP5.UnitTest-TestRunner1

01:39:19