fix mixture of sync/async sockets in IOPubThread #2593

Job	Run time
check_release	1m 51s
test_docs	40s
build (ubuntu-latest, 3.8)	56s
Test Lint	1m 6s
build (ubuntu-latest, 3.12)	1m 3s
Test Minimum Versions	57s
build (windows-latest, 3.8)	2m 48s
Test Prereleases	34s
build (windows-latest, 3.12)	2m 55s
test_without_debugpy (ubuntu-latest, 3.9)	35s
link_check	1m 37s
build (macos-latest, 3.8)	1m 24s
Make SDist	25s
build (macos-latest, 3.12)	1m 0s
build (windows-latest, 3.9)	2m 44s
build (ubuntu-latest, pypy-3.9)	1m 1s
build (macos-latest, 3.10)	52s
build (ubuntu-latest, 3.11)	48s
Install from SDist and Test	40s
coverage	0s
tests_check	4s
	24m 0s

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