Add unit tests for wp_refresh_metabox_loader_nonces() in wp-admin/inc… #29904

Job	Run time
Core running from build / MacOS	3m 18s
Core running from src / Windows	3m 28s
Core running from build / Linux	2m 52s
Core running from build / Windows	3m 45s
Core running from src / MacOS	3m 7s
Core running from src / Linux	2m 15s
Slack Notifications	0s
Failed workflow tasks	0s
	18m 45s

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