title: odoo get several data in text field
body: <p>I have this py script</p>
  <pre><code>@api.one
  @api.depends('customer_id')
  def _get_unpaid_list(self):
      invoice_pool = self.env['account.invoice']
      for rec in invoice_pool.search([('state', '=', 'open'), ('partner_id', '=', self.customer_id.id)]):
          amount_total = rec.amount_total or ''
          number = rec.number or ''
          name = ustr(amount_total) + &quot;-&quot; + ustr(number)
          self.unpaid_list = name
  unpaid_list = fields.Text(string=&quot;Customer Debt List&quot;, compute=&quot;_get_unpaid_list&quot;, )
  </code></pre>
  <p>and this xml</p>
  <pre><code>&lt;field name=&quot;unpaid_list&quot; /&gt;
  </code></pre>
  <p>It works with this output</p>
  <pre><code>19690000.0-INV/2021/13928
  </code></pre>
  <p>BUT it should show several line of data like this</p>
  <pre><code>19690000.0-INV/2021/13928
  25590000.0-INV/2021/13929
  23450000.0-INV/2021/13930
  </code></pre>
  <p>How to make a list of data like it should?
  Thank you</p>