Use `env!("CARGO_CRATE_NAME")` in the example to simplify the tracing setup code #4713

Job	Run time
check-docs	36s
cargo-hack	5m 46s
cargo-public-api-crates (axum)	38s
check	1m 43s
cargo-public-api-crates (axum-core)	22s
cargo-deny check (advisories)	27s
cargo-public-api-crates (axum-extra)	45s
cargo-deny check (bans licenses sources)	24s
dependencies-are-sorted	20s
cargo-public-api-crates (axum-macros)	19s
Spell Check with Typos	7s
test-docs	0s
test-msrv	0s
test-nightly	0s
test-versions	0s
armv5te-unknown-linux-musleabi	0s
wasm32-unknown-unknown	0s
	11m 27s

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