Gnomes are given advantage on WIS saves against Magic. 4th Level Psionic Mystics (UA) have the ability to:
replace your proficiency in Wisdom saving throws whenever you finish a short or long rest. To do so, choose Strength, Dexterity, Constitution, or Charisma. You gain proficiency in saves using that ability, instead of Wisdom.
This allows you to make your WIS save using a different Ability Score, but do you still get the Gnome Advantage even though you're not using your Wisdom even though technically it is a WIS save?