Plumb EnvVars to subscription config builder to find duplicates (Azure#26944)

This will help avoid hard to diagnose issues where duplicate env var
values are being defined in multiple places.

Author: benbp

eng/pipelines/templates/jobs/live.tests.yml

@@ -72,6 +72,7 @@ jobs:
           parameters:
             SubscriptionConfiguration: ${{ parameters.CloudConfig.SubscriptionConfiguration }}
             SubscriptionConfigurations: ${{ parameters.CloudConfig.SubscriptionConfigurations }}
+            EnvVars: ${{ parameters.EnvVars }}
 
         - ${{ if parameters.TestResourceDirectories }}:
           - ${{ each directory in parameters.TestResourceDirectories }}: