Add warning about 3.0 #4650

Job	Run time
Tasks (latest) (3.12, ubuntu-22.04)	2m 43s
Tasks (latest) (3.7, ubuntu-22.04)	2m 36s
Tasks (pinned) (3.7, ubuntu-22.04)	4m 25s
Tasks (pinned) (3.8, ubuntu-22.04)	3m 35s
Tasks (latest) (3.13, ubuntu-22.04)	4m 0s
Tasks (latest) (3.8, ubuntu-22.04)	2m 20s
Tasks (pinned) (3.10, ubuntu-22.04)	3m 42s
Tasks (pinned) (3.13, ubuntu-22.04)	4m 51s
Tasks (latest) (3.11, ubuntu-22.04)	2m 42s
Tasks (latest) (3.10, ubuntu-22.04)	2m 21s
Tasks (pinned) (3.12, ubuntu-22.04)	5m 11s
Tasks (pinned) (3.9, ubuntu-22.04)	3m 17s
Tasks (pinned) (3.11, ubuntu-22.04)	4m 36s
All pinned Tasks tests passed	3s
	46m 22s

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