Add pool env variable to build-test-resource-config template (Azure#23111)

Author: benbp

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

@@ -77,7 +77,9 @@ jobs:
         parameters:
           SubscriptionConfiguration: ${{ parameters.CloudConfig.SubscriptionConfiguration }}
           SubscriptionConfigurations: ${{ parameters.CloudConfig.SubscriptionConfigurations }}
-          EnvVars: ${{ parameters.EnvVars }}
+          EnvVars:
+            Pool: $(Pool)
+            ${{ insert }}: ${{ parameters.EnvVars }}
 
       - template: /eng/common/TestResources/deploy-test-resources.yml
         parameters: