en,zh: add v1.6.4 release notes #8170

Job	Run time
check-unclosed-tags	10s
markdownlint	26s
check-control-characters	11s
verify-internal-link-anchors	18s
verify-internal-links	1m 35s
check-file-encoding	9s
check-manual-line-breaks	10s
check-git-conflicts	11s
	3m 10s

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