mesh_tissue: correct invalid annotation

typing.get_type_hints fails when setting the type to a string.

This has been commented in other uses, so it can be commented here too.

mesh_tissue/tessellate_numpy.py

@@ -1921,7 +1921,7 @@ class tessellate(Operator):
             max=1,
             description="Automatically set crease for open edges"
             )
-    working_on : ""
+    # working_on : ""
 
     def draw(self, context):
         allowed_obj = ('MESH', 'CURVE', 'SURFACE', 'FONT', 'META')