Threat Insights: Update verification steps for clarity

Why is this change being made?

There are a few potential gaps in our current verification policy:

1. The author is asked to unassign themselves before the change has hit .com. This means that the person assigned for production verification may need to proactively watch the MR to identify when it is testable. This effort is better suited for the author.
2. The author isn't asked to verify on production themselves.
3. The verifier may have trouble finding a suitable project to test against. It can be helpful for the author to provide a project. Especially for changes that require a unique project/group configuration.

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this MR to the correct Directly Responsible Individual/s (DRI)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the Maintained by section on the page being edited
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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