Improve the semantics of the disclosure content wrapper when it has custom content

The following discussion from gitlab!110683 (merged) should be addressed:

• @sdejonge started a discussion: (+2 comments)

  question: Can we remove this <div role="group">? I think the <slot> inside <gl-disclosure-dropdown> should already get an associated role from the computed <ul> or <div role="group">.

  The HTML output has <div> children of <ul> which is invalid.

  <ul id="disclosure-6" aria-labelledby="dropdown-toggle-btn-2" data-testid="disclosure-content" tabindex="-1" class="gl-new-dropdown-contents">
    <div>
      <ul role="group" class="gl-mb-0 gl-pl-0 gl-list-style-none">...</ul>
    </div>
    <div class="gl-border-t gl-pt-2 gl-mt-2">
      <ul role="group" class="gl-mb-0 gl-pl-0 gl-list-style-none">...</ul>
    </div>
    <div class="gl-border-t gl-pt-2 gl-mt-2">
      <ul role="group" class="gl-mb-0 gl-pl-0 gl-list-style-none">...</ul>
    </div>
  </ul>

  The isAllGroups util to set the parent as <div role="group"> checks the items but not the <slot> contents as in this case.

  question: would it be silly to make the root element of <gl-disclosure-dropdown-group> a <li> and always render the slot contents of <gl-disclosure-dropdown> in a <ul>? Or is there a better way to set the parent as <div role="group"> when the <slot> content only contains <gl-disclosure-dropdown-group>?