ENH Update code to reflect changes in silverstripe/admin #1006

Job	Run time
CI / Generate matrix	15s
CI / Context	1s
CI / Check governance	0s
CI / 8.3 prf-low mariadb phpunit all	2m 36s
CI / 8.3 mysql80 phpunit all	2m 37s
CI / 8.3 mysql80 phplinting	1m 36s
CI / 8.3 mysql80 endtoend root job1	13m 14s
CI / 8.3 mysql80 endtoend root job2	10m 11s
CI / 8.3 mysql80 endtoend root job3	8m 37s
CI / 8.3 mysql80 js	4m 0s
CI / Dispatch tag patch release	0s
	43m 7s

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