Media: improve speed of AVIF image generation. #9839

Job	Run time
Core running from build / Core running from build / Linux	2m 0s
Core running from src / Core running from src / Linux	1m 56s
Core running from build / Core running from build / Windows	3m 59s
Core running from src / Core running from src / Windows	3m 43s
Core running from build / Core running from build / MacOS	1m 36s
Core running from src / Core running from src / MacOS	1m 52s
Gutenberg running from build / Gutenberg running from build / Linux	7m 57s
Gutenberg running from src / Gutenberg running from src / Linux	7m 57s
Gutenberg running from build / Gutenberg running from build / Windows	11m 44s
Gutenberg running from src / Gutenberg running from src / Windows	11m 3s
Gutenberg running from build / Gutenberg running from build / MacOS	10m 27s
Gutenberg running from src / Gutenberg running from src / MacOS	7m 4s
Slack Notifications / Prepare notifications	3s
Slack Notifications / Failure notifications	0s
Slack Notifications / Fixed notifications	0s
Slack Notifications / Cancelled notifications	0s
Slack Notifications / Success notifications	3s
Failed workflow tasks	0s
	1h 11m 24s

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