Citing a math theorem with errors
Given the situation as you describe it, in particular that there is evidence that the author could have corrected the presumably-small mistake themselves, I'd recommend that you quote the true assertion, and/while noting, literally, that there is an easily correctible error or typo in the proof as written.

Catching typos is important, but is not "research", of course. And, yes, once typos or silly mis-statements are pointed out, many authors can repair them without hesitation. So I myself generally consider "paper X" to be "paper X with all trivial typos and obvious blunders corrected". (Still, yes, sometimes the boundary of this is not clear...)

In particular, yes, I give credit to authors for obtaining a result who've slightly messed up the argument, both for observing what is true, and for at least approximating the proof.