[FIX] purchase: corrects the order date on validated RFQ/PO pdf report

Expected behaviour

The order date on the Purchase Order report (printable pdf) should be the
confirmation date if available and the order deadline else.

Observed Behaviour

The order date on the PO pdf is the order deadline of the RFQ, no matter
if the oder has been confirmed or not.

Reproducibility

This issue can be reproduced following these steps:
1. Create a new RFQ
2. Set an order deadline different from the current day
3. Confirm the RFQ
4. Download the printable PDF (as pdf) and check the Order date

Related ticket
- opw-2696794

closes odoo/odoo#81294

Signed-off-by: William Henrotin (whe) <whe@odoo.com>

addons/purchase/report/purchase_order_templates.xml

@@ -35,8 +35,12 @@
                     <strong>Your Order Reference:</strong>
                     <p t-field="o.partner_ref" class="m-0"/>
                 </div>
-                <div t-if="o.date_order" class="col-3 bm-2">
+                <div t-if="o.state in ['purchase','done'] and o.date_approve" class="col-3 bm-2">
                     <strong>Order Date:</strong>
+                    <p t-field="o.date_approve" class="m-0"/>
+                </div>
+                <div t-elif="o.date_order" class="col-3 bm-2">
+                    <strong >Order Deadline:</strong>
                     <p t-field="o.date_order" class="m-0"/>
                 </div>
             </div>