docs: update PHPUnit testing README.md with corrections #62065 #9841

Job	Run time
Core running from build / Core running from build / Linux	2m 2s
Core running from src / Core running from src / Linux	1m 58s
Core running from build / Core running from build / Windows	4m 30s
Core running from src / Core running from src / Windows	4m 7s
Core running from build / Core running from build / MacOS	1m 40s
Core running from src / Core running from src / MacOS	2m 13s
Gutenberg running from build / Gutenberg running from build / Linux	7m 56s
Gutenberg running from src / Gutenberg running from src / Linux	7m 57s
Gutenberg running from build / Gutenberg running from build / Windows	10m 51s
Gutenberg running from src / Gutenberg running from src / Windows	11m 24s
Gutenberg running from src / Gutenberg running from src / MacOS	6m 51s
Gutenberg running from build / Gutenberg running from build / MacOS	6m 54s
Slack Notifications	0s
Failed workflow tasks	0s
	1h 8m 23s

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