Don't prepare the response body for HEAD requests #12993

Job	Run time
Core running from src / Core running from src / Linux	2m 3s
Core running from build / Core running from build / Linux	2m 14s
Core running from build / Core running from build / Windows	4m 1s
Core running from src / Core running from src / Windows	3m 55s
Core running from build / Core running from build / MacOS	2m 19s
Core running from src / Core running from src / MacOS	1m 47s
Gutenberg running from build / Gutenberg running from build / Linux	8m 44s
Gutenberg running from src / Gutenberg running from src / Linux	8m 34s
Gutenberg running from build / Gutenberg running from build / Windows	12m 10s
Gutenberg running from src / Gutenberg running from src / Windows	12m 29s
Gutenberg running from build / Gutenberg running from build / MacOS	7m 28s
Gutenberg running from src / Gutenberg running from src / MacOS	8m 48s
Slack Notifications	0s
Failed workflow tasks	0s
	1h 14m 32s

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