fix mixture of sync/async sockets in IOPubThread #2587

Job	Run time
Make SDist	24s
link_check	3m 29s
check_release	1m 47s
build (ubuntu-latest, 3.8)	58s
test_docs	39s
build (ubuntu-latest, 3.12)	58s
Test Lint	56s
Test Minimum Versions	58s
build (windows-latest, 3.8)	4m 52s
build (windows-latest, 3.12)	4m 33s
Test Prereleases	32s
test_without_debugpy (ubuntu-latest, 3.9)	36s
build (macos-latest, 3.8)	1m 26s
build (macos-latest, 3.12)	1m 15s
build (windows-latest, 3.9)	4m 40s
build (ubuntu-latest, pypy-3.9)	59s
build (macos-latest, 3.10)	57s
build (ubuntu-latest, 3.11)	58s
Install from SDist and Test	35s
coverage	0s
tests_check	4s
	31m 36s

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