fix DNS issues with unresolvable backends with ExternalName

[k8s-infra-cherrypick-robot]

This is an automated cherry-pick of #10989

/assign Gacko

[Gacko]

/retitle fix DNS issues with unresolvable backends with ExternalName
/triage accepted
/kind bug
/priority backlog
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Gacko, k8s-infra-cherrypick-robot

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[Gacko]

/retest

[k8s-ci-robot]

@k8s-infra-cherrypick-robot: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pre-ingress-nginx-lua-test	1b65a96	link	true	/test pre-ingress-nginx-lua-test

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[Gacko]

Lua Test is failing because we cannot define E2E Test Runner images per branch in the pre-submit jobs. There's only one job and one image. The current E2E Test Runner image was built on top of an NGINX base image version which already no longer contains the Global Throttle feature. We therefore need to ignore the Lua Test check.