Literacy tests have historically been a way of disenfranchising minority (typically black) voters, so just think of a worse version of that. Also as other people have said most politicians are very well-educated as is. More fundamentally, though, restricting political participation in this way runs directly counter to what democracy is; the question that needs to be asked is “is there a dire problem you’re solving by compromising democracy in this way” and the answer is “no.”