Make into_future on Serve, WithGracefulShutdown independent of tokio #4913

Job	Run time
cargo-hack	5m 48s
check	1m 30s
check-docs	21s
cargo-public-api-crates (axum)	32s
cargo-public-api-crates (axum-core)	16s
cargo-deny check (advisories)	23s
cargo-public-api-crates (axum-extra)	30s
cargo-deny check (bans licenses sources)	31s
dependencies-are-sorted	13s
cargo-public-api-crates (axum-macros)	18s
Spell Check with Typos	6s
armv5te-unknown-linux-musleabi	56s
test-docs	1m 37s
test-nightly	1m 31s
test-msrv	1m 52s
test-versions (stable)	2m 41s
wasm32-unknown-unknown	12s
test-versions (beta)	2m 41s
	21m 58s

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