Media: Clarify caption field labels for images and videos #29425

Job	Run time
Core running from build / Linux	2m 27s
Core running from src / Windows	3m 27s
Core running from build / MacOS	2m 44s
Core running from build / Windows	3m 43s
Core running from src / Linux	2m 14s
Core running from src / MacOS	2m 46s
Slack Notifications	0s
Failed workflow tasks	0s
	17m 21s

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