Posts, Post Types: Fix missing array check in get_post_custom_values(). #28703

Job	Run time
Core running from src / Linux	2m 17s
Core running from build / Linux	2m 17s
Core running from build / MacOS	2m 11s
Core running from src / MacOS	2m 29s
Core running from src / Windows	3m 16s
Core running from build / Windows	3m 11s
Slack Notifications	0s
Failed workflow tasks	0s
	15m 41s

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