[react] HeaderSideNavItems does not apply className passed as a prop

[zevioso]

What package(s) are you using?

• carbon-components
• carbon-components-react

Detailed description

Describe in detail the issue you're having.

When passing a className prop to the HeaderSideItems component, the class is not applied instead customClassName is added as a class to the element.

Is this issue related to a specific component?
HeaderSideNavItems - https://github.com/carbon-design-system/carbon/blob/master/packages/react/src/components/UIShell/HeaderSideNavItems.js

What did you expect to happen? What happened instead? What would you like to
see changed?

The className prop that I pass should be applied.

What browser are you working in?

Chrome, Firefox, Safari

What version of the Carbon Design System are you using?

10.9.2

Steps to reproduce the issue

1. Add className="test" to <HeaderSideNavItems />

Please create a reduced test case in CodeSandbox

https://codesandbox.io/s/frosty-banach-ny7is?fontsize=14&hidenavigation=1&theme=dark

Additional information