Update Rust crate toml to v0.8.20 #40317

Job	Run time
cargo fmt	20s
mkdocs	2m 54s
Determine changes	12s
cargo build (release)	0s
pre-commit	3m 27s
python package	1m 42s
benchmarks	5m 11s
cargo fuzz build	4m 51s
cargo build (msrv)	2m 1s
cargo clippy	2m 27s
cargo shear	23s
cargo test (linux)	2m 12s
cargo test (linux, release)	4m 8s
cargo test (wasm)	1m 58s
cargo test (windows)	5m 17s
formatter instabilities and black similarity	3m 42s
test scripts	1m 11s
test ruff-lsp	47s
fuzz parser	5m 38s
ecosystem	4m 26s
	52m 47s

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