fix: exclude unmanaged route parents from xPolicy status ancestors

[zhaohuabing]

This PR fixes xPolicy route-target status ancestors for mixed managed and unmanaged parentRefs.

When an HTTPRoute has both:

• a parent Gateway managed by Envoy Gateway, and
• a parent Gateway from a different GatewayClass,

xPolicy.status.ancestors should only include the Envoy Gateway-managed parent(s).
Before this change, unmanaged parents could appear in xPolicy.status.ancestors.

Example:

Given:

• managed-gateway with gatewayClassName: envoy-gateway-class
• unmanaged-gateway with gatewayClassName: other-gateway-class
• HTTPRoute mixed-parents-route with both parentRefs
• SecurityPolicy route-policy targeting mixed-parents-route

Before this PR, SecurityPolicy.status.ancestors could include both gateways:

status:
  ancestors:
  - ancestorRef:
      name: managed-gateway
      kind: Gateway
      group: gateway.networking.k8s.io
      namespace: default
      sectionName: http
  - ancestorRef:
      name: unmanaged-gateway
      kind: Gateway
      group: gateway.networking.k8s.io
      namespace: default
      sectionName: http

After this PR, only EG-managed ancestors are reported:

  status:
    ancestors:
    - ancestorRef:
        name: managed-gateway
        kind: Gateway
        group: gateway.networking.k8s.io
        namespace: default
        sectionName: http

Fixes: #8320

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.67%. Comparing base (7031394) to head (d5ea0a4).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8321      +/-   ##
==========================================
+ Coverage   73.66%   73.67%   +0.01%     
==========================================
  Files         242      242              
  Lines       37007    37014       +7     
==========================================
+ Hits        27261    27270       +9     
  Misses       7826     7826              
+ Partials     1920     1918       -2     

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[zhaohuabing]

The unmanaged-gateway should not be in status.

[kkk777-7]

LGTM, thanks!