Fix undefined method exception

What does this MR do and why?

• Contributes to #382274 (closed)
• Sentry error: https://sentry.gitlab.net/gitlab/gitlabcom/issues/3313547

Problem

We report "undefined method" exception to Sentry for each missing HLL event.

Solution

Add a validation for event type to avoid unnecessary noise in Sentry.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.