ENH Update code to reflect changes to silverstripe/admin #999

Job	Run time
CI / Context	1s
CI / Generate matrix	19s
CI / Check governance	0s
CI / 8.3 prf-low mariadb phpunit all	2m 34s
CI / 8.3 mysql80 phpunit all	2m 59s
CI / 8.3 mysql80 phplinting	1m 46s
CI / 8.3 mysql80 endtoend root job1	9m 19s
CI / 8.3 mysql80 endtoend root job2	8m 28s
CI / 8.3 mysql80 endtoend root job3	6m 36s
CI / 8.3 mysql80 js	4m 26s
CI / Dispatch tag patch release	0s
	36m 28s

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