Fix PrivateCookieJar documentation example comments #5064

Job	Run time
check-docs	35s
cargo-public-api-crates (axum)	30s
check	40s
cargo-hack	6m 10s
cargo-public-api-crates (axum-core)	26s
cargo-public-api-crates (axum-extra)	34s
cargo-deny check (advisories)	27s
dependencies-are-sorted	32s
cargo-public-api-crates (axum-macros)	16s
Spell Check with Typos	6s
cargo-deny check (bans licenses sources)	33s
test-msrv	0s
armv5te-unknown-linux-musleabi	0s
test-docs	0s
test-nightly	0s
test-versions	0s
wasm32-unknown-unknown	0s
	10m 49s

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