How can I skip my attack?
No, there's no option to skip an attack.
What you can do is either use a Power Potion and then a spell (items are a 'free' action, and there's really no point in hoarding consumables), or use the 'Switch Buddy' command to swap in a different team member with a ranged attack, such as Kenny.
Alternately, just eat the Riposte. Honestly, they usually don't do that much damage. Butters can handle it.