Update gitlab-experiment to version 0.5.4

What does this MR do?

Updates gitlab-experiment to 0.5.4.

To review the gem updates, please check and feel free to review the release MR, which has more information.

Please note that a good chunk of the linked MR is in release tooling changes. We use each release as an opportunity to automate or improve the process where we can, and those aren't included in the gem.

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because largely tooling.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

I don't foresee very many risks here. There are also several tracking updates that will follow this MR -- one to anonymize better, and another to utilize better RequestStore utilization and to resolve render order issues with Gon.