Update and fix mongo example #5850

Job	Run time
check-docs	44s
check	2m 8s
cargo-hack	6m 6s
dependencies-are-sorted	4s
cargo-public-api-crates (axum-core)	37s
cargo-public-api-crates (axum-extra)	45s
cargo-public-api-crates (axum)	52s
cargo-public-api-crates (axum-macros)	37s
Spell Check with Typos	7s
cargo-deny check (advisories)	24s
cargo-deny check (bans licenses sources)	25s
test-nightly	1m 29s
test-versions (stable)	3m 41s
test-versions (beta)	3m 31s
test-msrv	2m 40s
test-docs	1m 37s
armv5te-unknown-linux-musleabi	1m 7s
wasm32-unknown-unknown	24s
	27m 18s

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