[FIX] purchase: Prevents logging a qty update when qty isn't updated

closes odoo/odoo#110905

X-original-commit: dbf526ba37e0e34a569aee079e4cd65b24a6d6d0
Signed-off-by: William Henrotin (whe) <whe@odoo.com>

addons/purchase/models/purchase.py

@@ -1096,13 +1096,18 @@ class PurchaseOrderLine(models.Model):
             raise UserError(_("You cannot change the type of a purchase order line. Instead you should delete the current line and create a new line of the proper type."))
 
         if 'product_qty' in values:
+            precision = self.env['decimal.precision'].precision_get('Product Unit of Measure')
             for line in self:
-                if line.order_id.state == 'purchase':
+                if (
+                    line.order_id.state == "purchase"
+                    and float_compare(line.product_qty, values["product_qty"], precision_digits=precision) != 0
+                ):
                     line.order_id.message_post_with_source(
                         'purchase.track_po_line_template',
                         render_values={'line': line, 'product_qty': values['product_qty']},
                         subtype_xmlid='mail.mt_note',
                     )
+
         if 'qty_received' in values:
             for line in self:
                 line._track_qty_received(values['qty_received'])