Rust

minor: simplify `union_extract` code #38518

Job	Run time
Check License Header	2m 29s
linux build test	5m 12s
build with wasm-pack	3m 35s
Check cargo fmt	41s
cargo test (macos-aarch64)	9m 18s
Verify Vendored Code	53s
Verify MSRV (Min Supported Rust Version)	8m 4s
cargo check functions	2m 15s
cargo check datafusion	3m 44s
cargo doc	3m 48s
cargo check no default features	3m 47s
cargo test (amd64)	3m 49s
cargo test doc (amd64)	3m 48s
check Cargo.toml formatting	3m 47s
cargo examples (amd64)	3m 49s
clippy	3m 47s
check configs.md and ***_functions.md is up-to-date	3m 48s
Run sqllogictest with Postgres runner	3m 47s
cargo test pyarrow (amd64)	3m 42s
verify benchmark results (amd64)	3m 44s
	1h 17m 47s

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