Rust

minor: fix cargo clippy some warning #1012

Job	Run time
cargo check	3m 17s
build with wasm-pack	2m 30s
cargo test (macos)	25m 58s
cargo test (macos-aarch64)	8m 24s
Check cargo fmt	45s
Verify MSRV (Min Supported Rust Version)	7m 9s
Verify Vendored Code	55s
cargo test (win64)	32m 58s
cargo test (amd64)	10m 51s
cargo test datafusion-cli (amd64)	3m 35s
cargo examples (amd64)	9m 33s
check Cargo.toml formatting	2m 59s
clippy	5m 51s
check configs.md is up-to-date	2m 18s
cargo test hash collisions (amd64)	9m 56s
cargo doc	4m 44s
cargo test doc (amd64)	12m 55s
Run sqllogictest with Postgres runner	3m 7s
cargo test pyarrow (amd64)	2m 34s
verify benchmark results (amd64)	10m 9s
	2h 40m 28s

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