Upgrade tokio-tungstenite to 0.21 (#2435) #4178

Job	Run time
cargo-hack	3m 18s
check-docs	38s
check	56s
cargo-public-api-crates (axum)	1m 2s
cargo-public-api-crates (axum-core)	50s
cargo-deny check (advisories)	26s
Spell Check with Typos	4s
cargo-deny check (bans licenses sources)	22s
dependencies-are-sorted	20s
cargo-public-api-crates (axum-extra)	55s
cargo-public-api-crates (axum-macros)	49s
test-docs	1m 46s
test-nightly	1m 52s
armv5te-unknown-linux-musleabi	32s
test-msrv	4m 27s
test-versions (stable)	2m 23s
wasm32-unknown-unknown	21s
test-versions (beta)	2m 19s
	23m 20s

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