Boost Geo prune worker to run every 2 hours instead of 6

What does this MR do?

Changes cron schedule for geo_prune_event_log_worker from 0 */6 * * * to 0 */2 * * *.

Why was this MR needed?

It reduces the average of 600k events deleted every 6h, to 200k events deleted every 2h: https://gitlab.com/gitlab-com/infrastructure/issues/4231#note_79874454

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• EE specific content should be in the top level /ee folder
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes gitlab-com/infrastructure#4231