Fixing branch name logic.
Fixing branch name logic.

* The existing logic didn't account for a branch name being "release/3.1.0"
* We leveraged the azure devops variable 'Build.SourceBranchName' which returned the "last path segment in the ref string".

dotnet/wcf,dotnet/wcf,mconnew/wcf,imcarolwang/wcf,StephenBonikowsky/wcf,mconnew/wcf,imcarolwang/wcf,imcarolwang/wcf,dotnet/wcf,mconnew/wcf,StephenBonikowsky/wcf