(4.x) Merge 3.4

[alalek]

#21785 from alalek:python_fix_subclass_order
#21794 from yash112-lang:3.4
#21795 from alalek:dnn_test_update_openvino_3.4
#21798 from gititgo:4.x

Previous "Merge 3.4": #21784

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[alalek]

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