Update example reverse-proxy to axum 0.7 (#2395) #4130

Job	Run time
cargo-hack	3m 13s
check	2m 17s
check-docs	30s
cargo-public-api-crates (axum)	1m 4s
cargo-public-api-crates (axum-core)	51s
cargo-deny check (advisories)	25s
cargo-public-api-crates (axum-extra)	57s
dependencies-are-sorted	44s
cargo-deny check (bans licenses sources)	28s
cargo-public-api-crates (axum-macros)	53s
Spell Check with Typos	7s
test-docs	2m 9s
armv5te-unknown-linux-musleabi	1m 2s
test-nightly	2m 9s
test-msrv	7m 48s
test-versions (stable)	3m 25s
wasm32-unknown-unknown	23s
test-versions (beta)	4m 34s
	32m 59s

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