os/mac/diagnostic: fix OpenCore check #31221

Job	Run time
syntax	48s
cask audit	2m 26s
tap syntax	7m 15s
formula audit	4m 33s
test default formula (Ubuntu 22.04)	1m 43s
test default formula (Ubuntu 20.04)	2m 46s
update-test (Ubuntu)	23s
tests (online)	5m 22s
test default formula (macOS 13 x86_64)	3m 25s
update-test (macOS)	23s
vendored gems	42s
tests (generic OS)	3m 8s
test default formula (macOS 15 arm64)	1m 33s
tests (Ubuntu 24.04)	3m 9s
tests (Ubuntu 22.04)	2m 57s
tests (Ubuntu 20.04)	3m 56s
tests (macOS 13 x86_64)	8m 56s
tests (macOS 15 arm64)	4m 53s
	58m 18s

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