fix(http1): send 'connection: close' during graceful shutdown #2782

Job	Run time
Check Style	7s
semver	12s
Verify hyper.h is up to date	26s
Check MSRV	59s
Test stable on ubuntu-latest	1m 7s
features	36s
Test C API (FFI)	30s
Test stable on windows-latest	1m 4s
Test stable on macOS-latest	1m 3s
minimal-versions	25s
Test with Miri	2m 18s
udeps	24s
Test beta on ubuntu-latest	1m 19s
Test beta on windows-latest	1m 29s
Test beta on macOS-latest	1m 15s
Test nightly on ubuntu-latest	1m 14s
Test nightly on windows-latest	1m 4s
Test nightly on macOS-latest	1m 13s
Build docs	0s
Check exposed types	0s
CI is green	0s
	16m 45s

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