Update gitlab experiment 0.5.1 [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

This update includes a notable bug fix for #324076 (closed)

To look at the other aspects that have been updated and reviewed, you can review the diffs at https://gitlab.com/gitlab-org/gitlab-experiment/-/compare/v0.5.0...release-0.5.1.

Does this MR meet the acceptance criteria?

Conformity

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