[FIX] stock_dropshipping: Creating a quotation without purchase permission

Fine tuning of this commit: f93fcaff

Steps to reproduce the bug:

- Open runbot v11
- Restrict Demo's access to Sales Manager for sales and employee for Employee
- Try to create a new quotation

Bug:
- You got Odoo server Error
Sorry, you are not allowed to access this document. Only users with the following access level are currently allowed to do that:
- Inventory/User
- Accounting & Finance/Billing
- Purchases/User
- Purchases/Manager
- Other Extra Rights/Portal
(Document model: purchase.order.line) - (Operation: read, User: 5)

opw:2120692

closes odoo/odoo#40094

Signed-off-by: Simon Goffin (sig) <sig@openerp.com>

addons/stock_dropshipping/views/sale_order_views.xml

@@ -6,6 +6,7 @@
             <field name="name">sale.order.form.sale.dropshipping</field>
             <field name="model">sale.order</field>
             <field name="inherit_id" ref="sale.view_order_form"/>
+            <field name="groups_id" eval="[(4, ref('purchase.group_purchase_user'))]"/>
             <field name="arch" type="xml">
                 <xpath expr="//page/field[@name='order_line']/form//field[@name='product_updatable']" position="after">
                     <field name="purchase_line_ids" invisible="1"/>