Bump golang.org/x/sync from 0.8.0 to 0.9.0 #1145

Job	Run time
quicktests	40s
lint	37s
coverage	53s
unittests (ubuntu-22.04)	1m 32s
unittests (ubuntu-latest-arm-8-cores)	2m 50s
unittests (macos-13)	1m 55s
unittests (self-hosted, macos, arm64)	48s
unittests (windows-2022)	3m 23s
Build postcli (ubuntu-22.04)	26s
Build postcli (ubuntu-latest-arm-8-cores)	1m 15s
Build postcli (macos-13)	38s
Build postcli (self-hosted, macos, arm64)	15s
Build postcli (windows-2022)	2m 29s
Publish release	0s
	17m 41s

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