Media: prevent uploading image types the server doesn’t support. #2085

Job	Run time
Single site report / PHP 8.3 with MySQL 8.4	48m 8s
Multisite report / PHP 8.3 with MySQL 8.4 multisite	47m 52s
Slack Notifications / Prepare notifications	4s
Slack Notifications / Success notifications	1s
Slack Notifications / Cancelled notifications	0s
Slack Notifications / Failure notifications	0s
Slack Notifications / Fixed notifications	0s
Failed workflow tasks	0s
	1h 36m 5s

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