ENH Update code to reflect changes in silverstripe/admin (#3024) #999

Job	Run time
CI / Generate matrix	19s
CI / Context	1s
CI / Check governance	1s
CI / 8.3 prf-low mariadb phpunit all	2m 47s
CI / 8.3 mysql80 phpunit all	3m 35s
CI / 8.3 mysql84 phpunit all	3m 8s
CI / 8.3 mysql80 phplinting	1m 47s
CI / 8.3 mysql80 endtoend root job1	8m 33s
CI / 8.3 mysql80 endtoend root job2	6m 27s
CI / 8.3 mysql80 endtoend root job3	6m 47s
CI / 8.3 mysql80 js	4m 25s
CI / Dispatch tag patch release	2s
	37m 52s

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