doc(lib): resolve rustdoc warning #2224

Job	Run time
Check Style	5s
Verify hyper.h is up to date	21s
features	22s
Test with Miri	58s
Test C API (FFI)	43s
Check MSRV	31s
Test stable on ubuntu-latest	1m 39s
udeps	31s
Test stable on windows-latest	4m 6s
Test stable on macOS-latest	2m 10s
Test beta on ubuntu-latest	1m 50s
Test beta on windows-latest	3m 4s
Test beta on macOS-latest	1m 26s
Test nightly on ubuntu-latest	1m 46s
Test nightly on windows-latest	3m 16s
Test nightly on macOS-latest	1m 34s
Build docs	22s
Check exposed types	35s
CI is green	1s
	25m 20s

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