Fix typo in extractors guide #5857

Job	Run time
check-docs	46s
cargo-deny check (bans licenses sources)	23s
cargo-hack	6m 7s
cargo-deny check (advisories)	24s
check	38s
dependencies-are-sorted	5s
cargo-public-api-crates (axum-core)	37s
cargo-public-api-crates (axum)	55s
cargo-public-api-crates (axum-extra)	48s
Spell Check with Typos	9s
cargo-public-api-crates (axum-macros)	37s
test-versions (beta)	1m 14s
test-nightly	1m 15s
test-versions (stable)	3m 39s
test-docs	1m 30s
wasm32-unknown-unknown	26s
test-msrv	2m 42s
armv5te-unknown-linux-musleabi	1m 3s
	23m 18s

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