Fix misleading release manager error message
Fix misleading release manager error message

jskeet/google-cloud-dotnet,jskeet/google-cloud-dotnet,jskeet/gcloud-dotnet,googleapis/google-cloud-dotnet,jskeet/google-cloud-dotnet,jskeet/google-cloud-dotnet,jskeet/google-cloud-dotnet,googleapis/google-cloud-dotnet,googleapis/google-cloud-dotnet