Update and fix mongo example (#3549) #5851

Job	Run time
dependencies-are-sorted	7s
check	2m 18s
cargo-hack	6m 24s
check-docs	52s
cargo-deny check (advisories)	30s
Spell Check with Typos	9s
cargo-deny check (bans licenses sources)	41s
cargo-public-api-crates (axum-core)	42s
cargo-public-api-crates (axum-macros)	40s
cargo-public-api-crates (axum)	57s
cargo-public-api-crates (axum-extra)	51s
test-nightly	1m 31s
test-versions (beta)	3m 45s
test-versions (stable)	3m 45s
test-docs	1m 40s
armv5te-unknown-linux-musleabi	1m 10s
test-msrv	2m 51s
wasm32-unknown-unknown	29s
	29m 22s

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