Fix the deprecated_properties method

What does this MR do and why?

This MR fix the deprecated_properties method introduced by MR !146520 (merged) to work with approval_policies.

More context can be found in this thread.

Related to #446268

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

1. Enable the feature flag

echo "Feature.enable(:security_policies_breaking_changes)" | rails c

2. Create a new project
3. Add a new member to the project with developer access
4. Go to Secure > Policies
5. Click on New policy
6. Select Merge request approval policy
7. Change to .yaml mode
8. Copy the yaml below:

type: approval_policy
name: Deny MIT
enabled: true
rules:
  - type: license_finding
    match_on_inclusion: true
    license_types:
      - MIT License
    license_states:
      - newly_detected
    branch_type: default
actions:
  - type: require_approval
    approvals_required: 1
    role_approvers:
      - developer

9. Click on Configure with a merge request
10. Merge the new MR to add the policy
11. Go to /-/graphql-explorer
12. Add a query like:

{
  project(fullPath: "root/test-mr-146520") {
    approvalPolicies {
      nodes {
        name
        deprecatedProperties
      }
    }
  }
}

13. Verify the deprecatedProperties is ["match_on_inclusion", "newly_detected"]
14. Go to Secure > Policies
15. Update the policy with the content below to remove the deprecated fields :

type: approval_policy
name: Deny MIT
enabled: true
rules:
  - type: license_finding
    match_on_inclusion_license: true
    license_types:
      - MIT License
    license_states:
      - detected
    branch_type: default
actions:
  - type: require_approval
    approvals_required: 1
    role_approvers:
      - developer

16. Repeat the steps 11 and 12
17. Verify the deprecatedPolicy is empty