CIconButton does not pass class correctly

[Sybren W]

Describe the bug
A clear and concise description of what the bug is.
When I add a CSS class to the CIconButton it doesn't show this class when the component is rendered.

To Reproduce
Steps to reproduce the behavior:

1. Add a class to the CIconButton component
2. <c-icon-button class="burger-button" aria-label="Burger menu" icon="hamburger" />`

4. No custom "burger-button" class

Expected behavior
I would expect the custom "burger-button" class to be the first in the row of the class prop.

Screenshots

Additional context
Inside the render function of the CIconButton component it seems like it's not passing the class prop.