If my Stupefy gets countered, will my Ravenbloom Student gain a Might from the countered Stupefy?

No, Ravenbloom Student will not gain +1 Might.

For Ravenbloom Student's ability to trigger, a spell must be played — and a spell is only considered "played" once it successfully resolves. If Stupefy is countered (by Defy, Windwall, Hard Bargain, etc.), it never resolves and was never "played" for the purposes of triggered abilities (Rule 425.1.b). The countered spell simply fizzles, the chain clears, and Ravenbloom Student's ability does not trigger.