Add conditions to test pipeline generation. (Azure#16675)

Co-authored-by: Mitch Denny <[email protected]>

Author: azure-sdk

eng/common/pipelines/templates/steps/prepare-pipelines.yml

@@ -71,6 +71,7 @@ steps:
         --debug
         ${{parameters.TestsConventionOptions}}
       displayName: Create Live Test pipelines for public repository
+      condition: ne(variables['TestsConventionOptions'],'')
       env:
         PATVAR: $(azuresdk-azure-sdk-devops-pipeline-generation-pat)
 
@@ -131,5 +132,6 @@ steps:
         --no-schedule
         ${{parameters.TestsConventionOptions}}
       displayName: Create Live Test pipelines for private repository
+      condition: ne(variables['TestsConventionOptions'],'')
       env:
         PATVAR: $(azuresdk-azure-sdk-devops-pipeline-generation-pat)