Bump activemq.version from 5.18.3 to 6.1.5 #941

Job	Run time
build (ubuntu-latest, 17, Client, false)	2m 23s
build (ubuntu-latest, 17, Server, false)	2m 33s
build (ubuntu-latest, 17, Core, false)	2m 45s
build (ubuntu-latest, 17, External, false)	2m 27s
build (ubuntu-latest, 17, Check-Updated-License-Files, false)	2m 31s
build (ubuntu-latest, 17, Integration-Test, false)	2m 36s
build (ubuntu-latest, 21, Client, false)	2m 20s
build (ubuntu-latest, 21, Server, false)	2m 40s
build (ubuntu-latest, 21, Core, false)	2m 16s
build (ubuntu-latest, 21, External, false)	2m 18s
build (ubuntu-latest, 21, Check-Updated-License-Files, false)	2m 16s
build (ubuntu-latest, 21, Integration-Test, false)	2m 17s
	29m 22s

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