chore: Add permissions for CI with fork for testing #98

Job	Run time
CI / Generate matrix	17s
CI / Context	1s
CI / Check governance	0s
CI / 8.1 prf-low mysql57 phpunit silverstripe-composable-validators	2m 49s
CI / 8.2 mariadb phpunit silverstripe-composable-validators	2m 34s
CI / 8.3 mysql80 phpunit silverstripe-composable-validators	2m 50s
CI / 8.1 mysql57 phplinting	1m 46s
CI / 8.1 mysql57 js	5m 35s
CI / 8.1 mysql57 endtoend admin	23m 15s
CI / 8.2 mysql57 endtoend cms	17m 30s
CI / Dispatch tag patch release	0s
	56m 37s

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