Trim down the upgrade testing workflow. #12416

Job	Run time
Core running from build / Core running from build / Linux	2m 8s
Core running from src / Core running from src / Linux	1m 58s
Core running from build / Core running from build / Windows	3m 18s
Core running from src / Core running from src / Windows	4m 20s
Core running from build / Core running from build / MacOS	2m 43s
Core running from src / Core running from src / MacOS	2m 1s
Gutenberg running from build / Gutenberg running from build / Linux	8m 31s
Gutenberg running from src / Gutenberg running from src / Linux	8m 31s
Gutenberg running from build / Gutenberg running from build / Windows	10m 37s
Gutenberg running from src / Gutenberg running from src / Windows	10m 36s
Gutenberg running from build / Gutenberg running from build / MacOS	8m 32s
Gutenberg running from src / Gutenberg running from src / MacOS	10m 49s
Slack Notifications	1s
Failed workflow tasks	1s
	1h 14m 6s

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