[red-knot] Minor refactor of red_knot_vendored/build.rs #38539

Job	Run time
Determine changes	8s
cargo build (release)	0s
cargo fmt	22s
mkdocs	2m 24s
pre-commit	3m 11s
python package	1m 12s
cargo fuzz build	5m 18s
cargo clippy	1m 57s
cargo build (msrv)	4m 3s
benchmarks	5m 4s
cargo shear	21s
cargo test (linux)	1m 46s
cargo test (linux, release)	3m 43s
cargo test (wasm)	1m 35s
cargo test (windows)	4m 36s
formatter instabilities and black similarity	0s
test scripts	1m 4s
ecosystem	2m 44s
test ruff-lsp	36s
fuzz parser	0s
	40m 4s

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