Use code block for better formatting of rustdoc for PhysicalGroupBy #19194

Job	Run time
Check cargo fmt	55s
cargo check	3m 16s
build with wasm-pack	2m 32s
cargo test (mac)	10m 44s
Verify Vendored Code	1m 3s
cargo test (win64)	18m 19s
Verify MSRV	10m 46s
cargo test datafusion-cli (amd64)	4m 40s
cargo examples (amd64)	7m 39s
clippy	6m 54s
cargo test hash collisions (amd64)	16m 8s
cargo doc	6m 6s
cargo test (amd64)	12m 51s
cargo test doc (amd64)	16m 35s
Run sqllogictest with Postgres runner	4m 55s
cargo test pyarrow (amd64)	3m 21s
verify benchmark results (amd64)	16m 34s
check Cargo.toml formatting	1m 51s
check configs.md is up-to-date	3m 36s
	2h 28m 45s

Provide feedback