Specify created_at date for VSA stage event

What does this MR do and why?

Related to #356743 (comment 886941575)

Ensures we specify the created_at date for the test merge request to be used in the setup for the VSA stage table tests.

Screenshots or screen recordings

No visual changes

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.