Rust

Fix compilation of `egui_extras` without `serde` feature #12440

Job	Run time
Check wasm32 + wasm-bindgen	2m 48s
android	35s
cargo-deny aarch64-apple-darwin	39s
cargo-deny aarch64-linux-android	42s
Format + check + test	3m 32s
ios	40s
cargo-deny i686-pc-windows-gnu	38s
cargo-deny i686-pc-windows-msvc	42s
Check Windows	2m 42s
cargo-deny i686-unknown-linux-gnu	40s
cargo-deny wasm32-unknown-unknown	37s
cargo-deny x86_64-apple-darwin	40s
cargo-deny x86_64-pc-windows-gnu	37s
cargo-deny x86_64-pc-windows-msvc	38s
cargo-deny x86_64-unknown-linux-gnu	38s
cargo-deny x86_64-unknown-linux-musl	36s
cargo-deny x86_64-unknown-redox	40s
	18m 4s

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