Improve `debug_handler` on tuple response types #3975

Job	Run time
cargo-hack	7m 1s
check	57s
check-docs	59s
cargo-public-api-crates (axum)	56s
cargo-public-api-crates (axum-core)	27s
cargo-deny check (advisories)	25s
dependencies-are-sorted	18s
cargo-deny check (bans licenses sources)	36s
cargo-public-api-crates (axum-extra)	29s
Spell Check with Typos	7s
cargo-public-api-crates (axum-macros)	13s
test-nightly	2m 19s
test-msrv	1m 59s
test-docs	2m 7s
armv5te-unknown-linux-musleabi	1m 21s
test-versions (stable)	3m 20s
wasm32-unknown-unknown	42s
test-versions (beta)	2m 40s
	26m 56s

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