fix: httpc connection close #724

Job	Run time
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/http3/admin)	16m 39s
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/plugin/[a-k]*)	34m 52s
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/plugin/[l-z]*)	35m 11s
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/admin t/cli t/config-center-yaml...	26m 40s
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/node t/pubsub t/router t/script ...	24m 31s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/http3/admin)	15m 11s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/plugin/[a-k]*)	35m 5s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/plugin/[l-z]*)	33m 59s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/admin t/cli t/config-center-yaml t/cont...	26m 23s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/node t/pubsub t/router t/script t/secre...	27m 42s
	4h 36m 13s

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