Fix rust-axum homepage toml quotes #654

Job	Run time
Build Rust (samples/client/petstore/rust/)	1m 14s
Build Rust (samples/client/others/rust/)	56s
Build Rust (samples/server/petstore/rust-server-deprecated/)	4m 11s
Build Rust (samples/server/petstore/rust-axum/)	2m 48s
Build Rust (samples/server/petstore/rust-server/)	3m 50s
	12m 59s

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