Add support for CMS 6 #26

Job	Run time
CI / Generate matrix	17s
CI / Context	2s
CI / 8.3 mysql80 phplinting	1m 48s
CI / 8.3 mysql80 endtoend root	3m 25s
CI / 8.3 mysql80 phpunit all	1m 46s
CI / Check governance	0s
CI / Dispatch tag patch release	0s
	7m 18s

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