Fix empty popover when pre-enforcement policy overrides setting

What does this MR do and why?

Fixes a bug in PolicyOverrideWarningIcon where a policy created before the enforcement_type field was introduced (pre-enforcement policy) could produce an empty popover.

Root cause: hasApprovalSettingsOverride was derived from policiesWithSettingsOverride.length > 0, but a pre-enforcement policy (no enforcement_type) passes the hasSettingsOverride check while failing both the enforced (=== 'enforce') and warn (=== 'warn') filters. This left the popover open with no content rendered.

Fix:

1. enforcedPoliciesWithSettingsOverride now includes policies where enforcement_type is absent — pre-enforcement policies default to the enforced behavior, which matches the original intent.
2. hasApprovalSettingsOverride is now derived from the two display-level computed properties (enforcedPoliciesWithSettingsOverride and warnPoliciesWithSettingsOverride) rather than the intermediate policiesWithSettingsOverride, eliminating any case where the icon shows but the popover is empty.

References

#590825 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable the security_orchestration_policies_configuration feature flag (or ensure scan result policies are available).
2. Set up a scan result policy on a project without an enforcement_type field in its YAML (i.e., a policy created before the enforcement_type field was added).
3. Navigate to Settings → Merge requests for that project.
4. Before this fix: the warning icon appears, clicking it opens an empty popover.
5. After this fix: the warning icon only appears when there is content to show; the popover correctly shows the policy in the enforced section.

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