[red-knot] Minor followup on str.startswith (#17362) #23

Job	Run time
Determine changes	14s
cargo build (release)	7m 33s
cargo fmt	20s
mkdocs	2m 39s
pre-commit	1d 0h 0m 0s
python package	1m 35s
cargo clippy	2m 9s
cargo test (linux)	1d 0h 0m 1s
cargo test (wasm)	1m 53s
cargo build (msrv)	1s
test scripts	1m 12s
cargo shear	30s
cargo test (linux, release)	1s
cargo fuzz build	4m 49s
cargo test (windows)	1d 0h 0m 1s
formatter instabilities and black similarity	3m 30s
benchmarks	0s
check playground	0s
test ruff-lsp	0s
fuzz parser	0s
ecosystem	0s
	3d 0h 26m 28s

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