ENH Update code to reflect changes to silverstripe/admin #415

Job	Run time
CI / Context	1s
CI / Generate matrix	22s
CI / Check governance	0s
CI / 8.3 prf-low mariadb phpunit all	2m 25s
CI / 8.3 mysql80 phpunit all	2m 22s
CI / 8.4 mysql84 phpunit all	2m 22s
CI / 8.3 mysql80 phplinting	1m 49s
CI / 8.3 mysql80 endtoend root	4m 41s
CI / 8.4 mysql84 endtoend root	3m 50s
CI / 8.3 mysql80 js	4m 3s
CI / Dispatch tag patch release	0s
	21m 55s

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