Add PR title format to `CONTRIBUTING.md` #26360

Job	Run time
pre-commit	30s
Determine changes	11s
cargo fmt	22s
mkdocs	2m 29s
python package	1m 19s
cargo test (linux)	0s
cargo test (wasm)	0s
cargo clippy	0s
cargo test (windows)	0s
cargo fuzz	0s
cargo udeps	0s
formatter instabilities and black similarity	0s
test scripts	0s
benchmarks	0s
ecosystem	0s
test ruff-lsp	0s
	4m 51s

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