Update variable groups for prepare-pipelines. (#44304)

See Azure/azure-sdk-tools#8359

Author: weshaggard

eng/pipelines/prepare-pipelines.yml

@@ -9,5 +9,5 @@ extends:
     Repository: $(Build.Repository.Name)
     Prefix: net
     CIConventionOptions: ''
-    UPConventionOptions: '--variablegroups 13 58 76 56 93'
+    UPConventionOptions: '--variablegroups 13 58 76 93'
     TestsConventionOptions: '--variablegroups 64'