axum: allow body types other than `axum::body::Body` in `Service`s passed to `serve` #5302

Job	Run time
check-docs	23s
cargo-hack	3m 14s
check	41s
cargo-public-api-crates (axum)	52s
cargo-deny check (advisories)	26s
dependencies-are-sorted	20s
Spell Check with Typos	3s
cargo-public-api-crates (axum-core)	38s
cargo-deny check (bans licenses sources)	21s
cargo-public-api-crates (axum-extra)	47s
cargo-public-api-crates (axum-macros)	36s
test-docs	1m 21s
test-versions (stable)	1m 14s
test-msrv	2m 37s
test-versions (beta)	1m 13s
armv5te-unknown-linux-musleabi	31s
test-nightly	1m 5s
wasm32-unknown-unknown	13s
	16m 35s

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