Clarify Drone CI error message based on configuration setting

Customer ticket: https://gitlab.zendesk.com/agent/tickets/46610

When you are using the Drone CI Service with Gitlab if you disable Merge Request Triggers on your project:

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When you create an Merge Request you will get an error suggesting that the issue is related to the CI server:

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It would be useful to change this message to something like "You've disabled Merge Request Triggers, enable them for Merge Request CI status".