Admin: Correct logic flow for nonce and capability checks in post.php #29423

Job	Run time
Core running from build / Linux	2m 28s
Core running from src / MacOS	2m 26s
Core running from src / Linux	2m 15s
Core running from src / Windows	3m 42s
Core running from build / Windows	3m 46s
Core running from build / MacOS	2m 53s
Slack Notifications	0s
Failed workflow tasks	0s
	17m 30s

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