[Backport 4.9] OF-2921: Prevent deadlock by not broadcasting synchronously #3507

Job	Run time
Check if database upgrade tests should be run	7s
Build Openfire from source (11, zulu)	14m 35s
check_branch	1s
Build Openfire from source (17, zulu)	14m 32s
Execute Connectivity CI tests	34s
Execute Smack-based CI tests	34s
Execute aioxmpp-based CI tests	1m 48s
Generate DEB artifact	3m 20s
Test MySQL Upgrades	0s
Test Postgres Upgrades	0s
Test SQL Server Upgrades	0s
Check if Docker Hub secrets exist	1s
Publish to Maven	0s
Publish to Docker Hub	0s
Test tagged images published to Docker Hub	0s
	35m 32s

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