fix lint errors in `loaders` #6962

Job	Run time
android	2s
Check wasm32 + wasm-bindgen	9m 25s
Format + check + test	11m 46s
cargo-deny aarch64-apple-darwin	4m 33s
cargo-deny aarch64-linux-android	2s
cargo-deny i686-pc-windows-gnu	1s
cargo-deny i686-pc-windows-msvc	4m 10s
cargo-deny i686-unknown-linux-gnu	4m 28s
cargo-deny wasm32-unknown-unknown	3m 49s
cargo-deny x86_64-apple-darwin	4m 45s
cargo-deny x86_64-pc-windows-gnu	3m 48s
cargo-deny x86_64-pc-windows-msvc	3m 22s
cargo-deny x86_64-unknown-linux-gnu	2s
cargo-deny x86_64-unknown-linux-musl	4m 12s
cargo-deny x86_64-unknown-redox	1s
Check Windows	1m 58s
	56m 24s

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