ENH Update code to reflect changes in silverstripe/admin #990

Job	Run time
CI / Context	1s
CI / Generate matrix	12s
CI / Check governance	0s
CI / 8.3 prf-low mariadb phpunit all	2m 41s
CI / 8.3 mysql80 phpunit all	2m 51s
CI / 8.3 mysql80 phplinting	1m 31s
CI / 8.3 mysql80 endtoend root job1	19m 47s
CI / 8.3 mysql80 endtoend root job2	14m 4s
CI / 8.3 mysql80 endtoend root job3	8m 1s
CI / 8.3 mysql80 js	4m 20s
CI / Dispatch tag patch release	0s
	53m 28s

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