Update istio test ref from main thread post branch cut

[ericvn]

Please provide a description for what this PR is for.

Update the istio test reference to latest master.

[ericvn]

/test lint

[ericvn]

/retest

[ericvn]

Interestingly, a local make lint passes.

[istio-testing]

@ericvn: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
lint_istio.io	13e8cef	link	true	/test lint
doc.test.multicluster_istio.io	13e8cef	link	true	/test doc.test.multicluster
doc.test.profile-none_istio.io	13e8cef	link	true	/test doc.test.profile-none
doc.test.profile-demo_istio.io	13e8cef	link	true	/test doc.test.profile-demo
doc.test.profile-minimal_istio.io	13e8cef	link	true	/test doc.test.profile-minimal
doc.test.profile-default_istio.io	13e8cef	link	true	/test doc.test.profile-default

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