Block Hooks: Fix child insertion next to Classic block #14277

Job	Run time
Core running from build / Core running from build / Linux	2m 8s
Core running from src / Core running from src / Linux	1m 59s
Core running from build / Core running from build / Windows	2m 27s
Core running from src / Core running from src / Windows	2m 19s
Core running from build / Core running from build / MacOS	2m 22s
Core running from src / Core running from src / MacOS	2m 13s
Gutenberg running from build / Gutenberg running from build / Linux	2m 32s
Gutenberg running from src / Gutenberg running from src / Linux	2m 32s
Gutenberg running from build / Gutenberg running from build / Windows	2m 28s
Gutenberg running from src / Gutenberg running from src / Windows	2m 28s
Gutenberg running from build / Gutenberg running from build / MacOS	2m 33s
Gutenberg running from src / Gutenberg running from src / MacOS	2m 34s
Slack Notifications	1s
Failed workflow tasks	1s
	28m 37s

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