ENH Update code to reflect changes in silverstripe/admin #1008

Job	Run time
CI / Generate matrix	22s
CI / Context	1s
CI / Check governance	0s
CI / 8.3 prf-low mariadb phpunit all	3m 8s
CI / 8.3 mysql80 phpunit all	2m 42s
CI / 8.3 mysql80 phplinting	1m 59s
CI / 8.3 mysql80 endtoend root job1	13m 21s
CI / 8.3 mysql80 endtoend root job2	10m 15s
CI / 8.3 mysql80 endtoend root job3	8m 45s
CI / 8.3 mysql80 js	5m 20s
CI / Dispatch tag patch release	0s
	45m 53s

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