GlDisclosureDropdown: Render `ul` when using custom components that wraps `<gl-discloure-dropdown-item/>`

Issue: Currently, the outer container renders <div/> instead of <ul/>, when using components that wrap ` in default slot.

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  <gl-disclosure-dropdown-group v-if="sshUrl">  
    <code-dropdown-item />
  </gl-disclousre-dropdown-group>?       

It looks like hasOnlyListItems checks that the slot contents must match gl-disclosure-dropdown-group, gl-disclosure-dropdown-item, or li, and code-dropdown-item does not match this even though it contains gl-disclosure-dropdown-item.