Use asyncio.Lock around subshell message handling #3597

Job	Run time
Test Lint	1m 4s
Test Prereleases	2m 31s
link_check	3m 18s
Make SDist	34s
test_without_debugpy (ubuntu-latest, 3.10)	2m 21s
Test Minimum Versions	2m 47s
check_release	1m 35s
build (ubuntu-latest, 3.13)	3m 19s
test_docs	56s
build (ubuntu-latest, 3.11)	3m 15s
build (ubuntu-latest, 3.10)	3m 14s
build (windows-latest, 3.11)	3m 18s
build (macos-latest, 3.12)	3m 20s
build (windows-latest, 3.12)	3m 17s
build (windows-latest, 3.10)	3m 17s
build (macos-latest, 3.10)	3m 21s
build (windows-latest, 3.13)	3m 18s
build (ubuntu-latest, pypy-3.10)	3m 18s
build (macos-latest, 3.11)	3m 20s
build (windows-latest, pypy-3.10)	3m 24s
build (macos-latest, pypy-3.10)	3m 21s
build (ubuntu-latest, 3.12)	3m 14s
build (macos-latest, 3.13)	3m 20s
Install from SDist and Test	2m 38s
coverage	1s
	1h 7m 21s

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