prevents brains from becoming bats (#62436)

PR'ed for Hacktoberfest (so if this passes muster I'd appreciate it being tagged with hacktoberfest-accepted)
really MMI's
closes Bat form lets you talk as a brain #62431
doesn't prevent borgs from becoming vampire bats

code/modules/spells/spell_types/shapeshift.dm

@@ -11,6 +11,7 @@
 	invocation = "RAC'WA NO!"
 	invocation_type = INVOCATION_SHOUT
 	action_icon_state = "shapeshift"
+	nonabstract_req = TRUE
 
 	var/revert_on_death = TRUE
 	var/die_with_shapeshifted_form = TRUE