Fix(sidebar): remove items attribute from li element

[annechko]

Hello!

Just found this little issue, it is happening right now in your demo:
https://coreui.io/demos/react/4.0/free/#/dashboard

In sidebar navigation, all li elements with nested lists look like this (they have extraitems attribute)

<li class="nav-group show" items="[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]"><a class="nav-link nav-group-toggle">

I wrote a test for this case, it doesn't pass in the current master branch but passes with the fix.
I need to test for attributes that are not visible to user, that's why I did as it said here:
https://testing-library.com/docs/queries/about/#manual-queries

But I was forced to ignore some linter warnings in the test file because it was complaining

  30:24  error  Avoid using container methods. Prefer using the methods from Testing Library, such as "getByRole()"  testing-library/no-container
  30:34  error  Avoid direct Node access. Prefer using the methods from Testing Library                              testing-library/no-node-access
  30:34  error  Avoid direct Node access. Prefer using the methods from Testing Library                              testing-library/no-node-access

Not the best decision, sorry, but I really wanted to add some tests!
What do you think? What can I do - rewrite the test, delete the test, delete the whole MR?...

[github-actions]

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