fix(http1): send 'connection: close' during graceful shutdown #2861

Job	Run time
semver	12s
Check Style	8s
Verify hyper.h is up to date	10s
Test with Miri	2m 28s
Check MSRV	18s
Test C API (FFI)	34s
features	28s
minimal-versions	28s
Test stable on ubuntu-latest	1m 7s
udeps	20s
Test stable on windows-latest	2m 59s
Test stable on macOS-latest	1m 3s
Test beta on ubuntu-latest	1m 11s
Test beta on windows-latest	2m 0s
Test beta on macOS-latest	1m 5s
Test nightly on ubuntu-latest	1m 25s
Test nightly on windows-latest	2m 36s
Test nightly on macOS-latest	2m 3s
Check exposed types	54s
Build docs	19s
CI is green	1s
	21m 49s

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