Update bot comment message for warn mode policy

What does this MR do and why?

Update bot comment message for warn mode policy

• add warn mode policies in additional info section

Changelog: changed

EE: true

References

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MR acceptance checklist

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Screenshots or screen recordings

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Scenario	without ff	with ff
warn mode policy		****

How to set up and validate locally

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

1. Upload a GitLab Ultimate license
2. Enable the feature flag echo "Feature.enable(:security_policy_approval_warn_mode)" | rails c
3. Navigate to a project => Secure => Policies => New policy => Merge request approval policy => Create a policy with a warn action
4. Navigate to the project and create an merge request that triggers the policy with the warn action
5. Verify the warn mode policy appears in the bot comment under the Additional Information section

Related to #512009 (closed)