ENH Update code to reflect changes to silverstripe/admin #982

Job	Run time
CI / Generate matrix	16s
CI / Context	1s
CI / Check governance	0s
CI / 8.3 prf-low mariadb phpunit all	2m 37s
CI / 8.3 mysql80 phpunit all	2m 42s
CI / 8.3 mysql80 phplinting	1m 32s
CI / 8.3 mysql80 endtoend root job1	8m 44s
CI / 8.3 mysql80 endtoend root job2	8m 54s
CI / 8.3 mysql80 endtoend root job3	6m 41s
CI / 8.3 mysql80 js	4m 20s
CI / Dispatch tag patch release	0s
	35m 47s

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