[release-1.3] Fix lint in the announcement

[istio-testing]

This is an automated cherry-pick of #5106

[googlebot]

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[istio-testing]

@istio-testing: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
lint_istio.io_release-1.3	c96f7a0	link	/test lint_istio.io_release-1.3

Details

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