BR v8.5.5: support br compact backup and prune field #8156

Job	Run time
markdownlint	27s
check-git-conflicts	13s
check-control-characters	12s
check-manual-line-breaks	10s
check-file-encoding	13s
verify-internal-link-anchors	20s
verify-internal-links	1m 43s
check-unclosed-tags	10s
	3m 28s

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