Use a stub rather than a real WorkflowJob instance in ScmResolverTest

[jglick]

CloudBees CI PCT runs indicate that this is broken by jenkinsci/jenkins#10042. Even on the current core version, it prints numerous stack traces because code is trying to run which cannot work in a Mockito-based environment. Please do not use Mockito to write tests for Jenkins plugins; it causes unnecessary maintenance burdens for others. I could not easily confirm the behavior directly on current core versions because of the use of the nonstandard analysis-pom parent POM; please use the standard parent instead (this is also a source of difficulty for the Jenkins community).

[uhafner]

@jglick do you need a new release or are the tests executed from the main branch?

[jglick]

A new release would be needed so we can update jenkinsci/bom to prepare for the weekly core release. Thanks!