Minor: format comments in `PushDownFilter` rule #26504

Job	Run time
Check cargo fmt	44s
cargo check	4m 21s
build with wasm-pack	2m 19s
cargo test (macos)	10m 33s
cargo test (macos-aarch64)	9m 54s
Verify MSRV (Min Supported Rust Version)	6m 45s
Verify Vendored Code	58s
cargo test (win64)	35m 43s
cargo test (amd64)	9m 42s
cargo examples (amd64)	11m 8s
cargo doc	3m 20s
cargo test datafusion-cli (amd64)	3m 37s
cargo test doc (amd64)	11m 25s
verify benchmark results (amd64)	10m 0s
check Cargo.toml formatting	2m 51s
clippy	4m 51s
check configs.md is up-to-date	2m 32s
cargo test hash collisions (amd64)	9m 5s
Run sqllogictest with Postgres runner	3m 11s
cargo test pyarrow (amd64)	2m 23s
	2h 25m 22s

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