Internal server error

Error:
    main is not enabled for this .ci.yaml.
    Add it to run tests against this PR.

Stack:
    #0      CiYaml.presubmitTargets (package:cocoon_service/src/model/ci_yaml/ci_yaml.dart:183:7)
    #1      CiYamlSet.presubmitTargets (package:cocoon_service/src/model/ci_yaml/ci_yaml.dart:85:22)
    #2      PresubmitLuciSubscription._getMaxAttempt (package:cocoon_service/src/request_handlers/presubmit_luci_subscription.dart:154:19)
    <asynchronous suspension>
    #3      PresubmitLuciSubscription.post (package:cocoon_service/src/request_handlers/presubmit_luci_subscription.dart:100:26)
    <asynchronous suspension>
    #4      RequestHandler.service (package:cocoon_service/src/request_handling/request_handler.dart:45:20)
    <asynchronous suspension>
    #5      SubscriptionHandler.service (package:cocoon_service/src/request_handling/subscription_handler.dart:140:5)
    <asynchronous suspension>
    #6      createServer.<anonymous closure> (package:cocoon_service/server.dart:317:7)
    <asynchronous suspension>