Make axum generic over it's Listener type #4417

Job	Run time
cargo-hack	24s
check-docs	37s
cargo-public-api-crates (axum)	58s
cargo-public-api-crates (axum-core)	47s
check	2m 5s
cargo-deny check (advisories)	23s
cargo-public-api-crates (axum-extra)	52s
dependencies-are-sorted	44s
cargo-deny check (bans licenses sources)	25s
cargo-public-api-crates (axum-macros)	48s
Spell Check with Typos	7s
test-docs	1m 57s
test-nightly	41s
armv5te-unknown-linux-musleabi	47s
wasm32-unknown-unknown	18s
test-versions (stable)	2m 39s
test-msrv	2m 50s
test-versions (beta)	4m 4s
	21m 26s

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