PRDOC: Document `validate: false` #17609

Job	Run time
check-dependency-rules	10s
check-fail-ci	12s
check-markdown	19s
check-readme	3m 8s
check-workspace	17s
preflight / preflight	1m 23s
preflight / ci-versions	1m 1s
check-rust-feature-propagation	2m 2s
fmt	1m 15s
test-rust-features	2m 4s
check-toml-format	1m 10s
check-umbrella	2m 24s
All quick checks passed	1s
	15m 26s

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