Tests: Add missing `@covers` tags for some oEmbed tests. #25585

Job	Run time
QUnit Tests / Run QUnit tests	2m 19s
Slack Notifications / Prepare notifications	6s
Slack Notifications / Success notifications	4s
Slack Notifications / Fixed notifications	0s
Slack Notifications / Cancelled notifications	0s
Slack Notifications / Failure notifications	0s
Failed workflow tasks	0s
	2m 29s

Provide feedback