Fix update of optional_approvals in bot comment

What does this MR do and why?

This change fixes a policy bot comment message in existing MRs in case the policy changes from having optional approvals to having required approvals

How to set up and validate locally

1. Create a policy which sets approvals_required: 0. Example YAML:

   type: scan_result_policy
   name: Secrets
   description: ''
   enabled: true
   rules:
     - type: scan_finding
       scanners:
         - secret_detection
       vulnerabilities_allowed: 0
       severity_levels: []
       vulnerability_states: []
       branch_type: protected
   actions:
     - type: require_approval
       approvals_required: 0
       user_approvers_ids:
         - 1

2. Create MR that violated the policy
3. Observe a bot comment that has optional_approvals section
4. Update the policy to set approvals_required: 1
5. Verify that bot comment message in the MR changes and optional_approvals section is removed

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.

Related to #420948 (closed)