wireframe/corner_set: fix luacheck warnings

worldeditadditions/lib/wireframe/corner_set.lua

@@ -12,8 +12,8 @@ function worldeditadditions.corner_set(pos1,pos2,node)
 	
 	-- z y x is the preferred loop order (because CPU cache I'd guess, since then we're iterating linearly through the data array)
 	local counts = { replaced = 0 }
-	for k,z in pairs({pos1.z,pos2.z}) do
-		for k,y in pairs({pos1.y,pos2.y}) do
+	for i,z in pairs({pos1.z,pos2.z}) do
+		for j,y in pairs({pos1.y,pos2.y}) do
 			for k,x in pairs({pos1.x,pos2.x}) do
 				minetest.set_node(vector.new(x,y,z), {name=node})
 				counts.replaced = counts.replaced + 1