[FIX] stock_manual_transfer: make demo route selectable

Since now only routes matching the selected warehouse are displayed [1],
the demo route should have the supplied warehouse set to be selectable.

[1]: 62ec4c4

stock_manual_transfer/demo/stock_demo.xml

@@ -15,6 +15,7 @@
         <field name="product_selectable" eval="True" />
         <field name="warehouse_selectable" eval="True" />
         <field name="manual_transfer_selectable" eval="True" />
+        <field name="supplied_wh_id" ref="demo_warehouse_01" />
     </record>
 
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