Replace "an ui" with "a ui" (#5185) #12898

Job	Run time
Check wasm32 + wasm-bindgen	2m 42s
Check wasm32+atomics	1m 35s
Format + check + test	5m 42s
android	21s
cargo-deny aarch64-apple-darwin	37s
ios	19s
cargo-deny aarch64-linux-android	38s
Check Windows	1m 54s
cargo-deny i686-pc-windows-gnu	52s
cargo-deny i686-pc-windows-msvc	38s
cargo-deny i686-unknown-linux-gnu	41s
cargo-deny wasm32-unknown-unknown	36s
cargo-deny x86_64-apple-darwin	41s
cargo-deny x86_64-pc-windows-gnu	36s
cargo-deny x86_64-pc-windows-msvc	35s
cargo-deny x86_64-unknown-linux-gnu	43s
cargo-deny x86_64-unknown-linux-musl	37s
cargo-deny x86_64-unknown-redox	39s
	20m 26s

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