Accordion and AccordionGroup ignore css_class attribute

[kosdmit]

the same issue as in crispy-bootstrap5: django-crispy-forms/crispy-bootstrap5#168

this layout:

test_form.helper.layout = Layout(
    Accordion(
        AccordionGroup("one", "first_name", css_class="one two three"),
        AccordionGroup("two", "password1", "password2"),
        css_class="four five"
    )
)

renders html which does not include css_class strings:

<form method="post">
  <div class="accordion" id="accordion-5422">
    <div class="accordion-group">
      <div class="accordion-heading">
        <a class="accordion-toggle" data-toggle="collapse" data-parent="#accordion-5422" href="#one">one</a>
      </div>
      <div id="one" class="accordion-body collapse in">
        <div class="accordion-inner">
          <div id="div_id_first_name" class="control-group">
            <label for="id_first_name" class="control-label requiredField">
              first name<span class="asteriskField">*</span> 
            </label>
            <div class="controls">
              <input type="text" name="first_name" maxlength="5" class="textinput textInput inputtext" required id="id_first_name">
            </div>
          </div>
        </div>
      </div>
    </div>

  </div>
</form>