Avoid flow to avoid the collection textfield from becoming too small

The collection instance field is currently using flow.column(), which makes the name of the collection instance unreadably small. {F6898084}
I get that we want to save vertical space to avoid scrolling, but in this case it generates a new problem, so I'd rather avoid flow here.

Patch by sebastian_k

Reviewed By: billreynish

Differential Revision: https://developer.blender.org/D4614

release/scripts/startup/bl_ui/properties_object.py

@@ -306,7 +306,7 @@ class OBJECT_PT_instancing(ObjectButtonsPanel, Panel):
             layout.prop(ob, "use_instance_vertices_rotation", text="Align to Vertex Normal")
 
         elif ob.instance_type == 'COLLECTION':
-            col = flow.column()
+            col = layout.column()
             col.prop(ob, "instance_collection", text="Collection")
 
         if ob.instance_type != 'NONE' or len(ob.particle_systems):