[instancer] Fix name decision-making

All limits are tuple these days.

Lib/fontTools/varLib/instancer/__init__.py

@@ -1549,7 +1549,7 @@ def main(args=None):
     )
 
     isFullInstance = {
-        axisTag for axisTag, limit in axisLimits.items() if not isinstance(limit, tuple)
+        axisTag for axisTag, limit in axisLimits.items() if limit[0] == limit[2]
     }.issuperset(axis.axisTag for axis in varfont["fvar"].axes)
 
     instantiateVariableFont(