fix: compile error on Unity 2021.2 or earlier (#753) #425

Job	Run time
K8s Tests (cloud-runner-end2end-locking)	3m 2s
K8s Tests (cloud-runner-environment)	3m 46s
K8s Tests (cloud-runner-github-checks)	1m 12s
K8s Tests (cloud-runner-end2end-retaining)	13m 26s
K8s Tests (cloud-runner-kubernetes)	7m 55s
AWS Tests (cloud-runner-end2end-caching)	29m 10s
AWS Tests (cloud-runner-environment)	2m 55s
AWS Tests (cloud-runner-end2end-locking)	2m 37s
AWS Tests (cloud-runner-end2end-retaining)	34m 45s
K8s Tests (cloud-runner-end2end-caching)	31m 5s
Tests (cloud-runner-end2end-caching)	7m 9s
Tests (cloud-runner-end2end-locking)	2m 13s
AWS Tests (cloud-runner-s3-steps)	29m 55s
Tests (cloud-runner-caching)	39s
Tests (cloud-runner-hooks)	4m 45s
Tests (cloud-runner-environment)	43s
Tests (cloud-runner-locking-get-locked)	5m 25s
Local Build Target Tests (local-docker, StandaloneOSX)	5m 0s
Tests (cloud-runner-end2end-retaining)	10m 26s
Tests (cloud-runner-image)	39s
Tests (cloud-runner-local-persistence)	48s
Local Build Target Tests (local-docker, StandaloneWindows64)	6m 56s
Local Build Target Tests (local-docker, WebGL)	7m 44s
Local Build Target Tests (local-docker, StandaloneLinux64)	4m 18s
Tests (cloud-runner-locking-core)	2m 5s
Local Build Target Tests (local-docker, iOS)	5m 22s
GitHub Checks Integration	0s
	3h 44m 0s

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