fix: content length assertion for HEAD #2908

Job	Run time
Verify hyper.h is up to date	26s
semver	13s
Check Style	5s
Test cargo-c support (FFI)	24s
Test C API (FFI)	36s
minimal-versions	30s
features	39s
Test with Miri	2m 39s
Check MSRV	29s
Test stable on ubuntu-latest	23s
udeps	24s
Test stable on windows-latest	33s
Test stable on macOS-latest	25s
Test beta on ubuntu-latest	32s
Test beta on windows-latest	25s
Test beta on macOS-latest	34s
Test nightly on ubuntu-latest	33s
Test nightly on windows-latest	25s
Test nightly on macOS-latest	38s
Check exposed types	0s
Build docs	0s
CI is green	0s
	10m 53s

Provide feedback