API Update code to reflect changes in silverstripe/cms #847

Job	Run time
CI / Generate matrix	20s
CI / Context	1s
CI / 8.3 prf-low mariadb phpunit all	1m 44s
CI / Check governance	0s
CI / 8.3 mysql80 phpunit all	2m 8s
CI / 8.4 mysql84 phpunit all	1m 47s
CI / 8.3 mysql80 phplinting	1m 37s
CI / 8.3 mysql80 endtoend root	3m 52s
CI / 8.4 mysql84 endtoend root	3m 13s
CI / 8.3 mysql80 js	1m 47s
CI / 8.3 mysql80 doclinting	1m 57s
CI / Dispatch tag patch release	0s
	18m 26s

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