Walmart wrote a $10 coupon for produce orders over $35. Nintendo fans figured out an $80 video game counts as produce if there's a single banana in the cart. The codes are FAST30 and SAVE3X, built to knock $10 off grocery hauls. The checkout logic apparently looks for two things, a produce item in the cart and $35 or more in total value. Fire Emblem: Fortune's Weave clears the dollar threshold by itself. The banana flips the category flag. A 20-cent piece of fruit unlocks a $10 discount, a…