It's just a test to understand how much they can get away with.

When Russia went into turkey airspace it took something like half a minute before they were shot down. They never touched that airspace again.

We don't even make a fuss about it, why shouldn't they test again? verify reactiveness, preparedness, populace and political reaction?

The less reaction there is, the less support for ukraine, too. Meaning they can ignore more "warfare laws" and other inconvenient stuff, like the peace talks.