fix: backend tls default namespace

[zhaohuabing]

Fixes: the default namespace for SecretObjectReference should be the owner namespace, not default.

The condition The Backend was not accepted: clientCertificateRef Secret is not located in the same namespace as Backend. Secret namespace: default does not match Backend namespace: httpbin-tls is wrong in the following example.

apiVersion: gateway.envoyproxy.io/v1alpha1
kind: Backend
metadata:
  name: httpbin-mtls-httpbin-tls-be
  namespace: httpbin-tls
  resourceVersion: "1768671158131743002"
  uid: 1cb357df-44b9-4204-87b0-dbeb4cf86b7d
spec:
  endpoints:
  - fqdn:
      hostname: httpbin-tls.httpbin-tls.svc.cluster.local
      port: 8443
  tls:
    caCertificateRefs:
    - group: ""
      kind: Secret
      name: httpbin-mtls-ssl
    clientCertificateRef:
      group: ""
      kind: Secret
      name: httpbin-mtls-ssl
      namespace: httpbin-tls
    insecureSkipVerify: false
  type: Endpoints
status:
  conditions:
  - lastTransitionTime: "2026-01-17T17:32:38Z"
    message: 'The Backend was not accepted: clientCertificateRef Secret is not located
      in the same namespace as Backend. Secret namespace: default does not match Backend
      namespace: httpbin-tls'
    observedGeneration: 2
    reason: Accepted
    status: "False"
    type: Invalid
  - lastTransitionTime: "2026-01-17T17:32:38Z"
    message: The Backend was accepted
    observedGeneration: 3
    reason: Accepted
    status: "True"
    type: Accepted

[netlify]

✅ Deploy Preview for cerulean-figolla-1f9435 canceled.

Name	Link
🔨 Latest commit	a6fe35d
🔍 Latest deploy log	https://app.netlify.com/projects/cerulean-figolla-1f9435/deploys/696dfc4501039d0008a8ed48

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.90%. Comparing base (844be64) to head (a6fe35d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7987      +/-   ##
==========================================
+ Coverage   72.86%   72.90%   +0.03%     
==========================================
  Files         237      237              
  Lines       35536    35536              
==========================================
+ Hits        25894    25907      +13     
+ Misses       7799     7791       -8     
+ Partials     1843     1838       -5     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[kkk777-7]

Just a question (not blocking):
Is there an EG coding rule about whether we should use ptr.Deref directly vs using a helper?

[kkk777-7]

LGTM, thanks!

[kkk777-7]

/retest