ENH Update code to reflect changes in silverstripe/admin #993

Job	Run time
CI / Generate matrix	27s
CI / Context	1s
CI / Check governance	0s
CI / 8.3 prf-low mariadb phpunit all	3m 14s
CI / 8.3 mysql80 phpunit all	3m 31s
CI / 8.3 mysql80 phplinting	1m 26s
CI / 8.3 mysql80 endtoend root job1	20m 1s
CI / 8.3 mysql80 endtoend root job2	14m 16s
CI / 8.3 mysql80 endtoend root job3	10m 10s
CI / 8.3 mysql80 js	3m 35s
CI / Dispatch tag patch release	0s
	56m 41s

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