Hard to find, but it's the kind of thing that will hopefully come up in code review. Consider this pseudocode with helpful pseudo-hungarian notation:

    username = request.post_params('username')
    evil_email = request.post_params('email_address')
    user = get_user_by_name(username)
    
    good_email = user.email_address
    if good_email != evil_email:
        # Hackers!
    else:
        reset_password(user.id, evil_email) # it's fine; it's the same as user.email_address

You can see the problem in the call to reset_password. Sure, it's the same as user.email_address, but if you just used user.email_address you'd be doing the right thing and you wouldn't need the comment about "don't worry; it's fine".

Then you start to wonder if that line shouldn't look more like

    reset_password(user)

and from a security perspective, it should. (I assume the reason Github allows the code to specify the email address in the first place is that an account may be associated with multiple addresses.)

If it makes no difference which email address you pick, why not pick the one that represents doing something safe instead of the one that represents doing something dangerous?