os/mac/diagnostic: fix OpenCore check #31218

Job	Run time
syntax	49s
formula audit	4m 31s
cask audit	2m 36s
tap syntax	6m 46s
test default formula (Ubuntu 22.04)	1m 21s
test default formula (Ubuntu 20.04)	2m 59s
tests (online)	5m 14s
test default formula (macOS 13 x86_64)	6m 15s
update-test (Ubuntu)	24s
tests (generic OS)	3m 8s
update-test (macOS)	32s
test default formula (macOS 15 arm64)	1m 38s
tests (Ubuntu 24.04)	2m 51s
vendored gems	40s
tests (Ubuntu 22.04)	2m 53s
tests (Ubuntu 20.04)	3m 45s
tests (macOS 13 x86_64)	10m 22s
tests (macOS 15 arm64)	4m 44s
	1h 1m 28s

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