[ic-side-navigation] - navigation group alignment issue

### Summary of the bug
When the side navigation includes a navigation group, the alignment is not centered vertically

### 🪜 How to reproduce
Tell us the steps to reproduce the problem:
1. Go to page: [side-nav expanded story](https://mi6.github.io/ic-ui-kit/branches/develop/react/?path=/story/react-components-side-navigation--side-nav-expanded-event)
2. focus the Navigation Group element
3. See the error:


Issue can also be seen on hover:


### 🧐 Expected behaviour
the text and icon should be centered vertically within the item

### 🚨 Urgency (low, medium or high)
Low

Start with the side-nav expanded story linked in the reproduction steps and inspect the Navigation Group rendered there, including its focus and hover states. Compare the text and icon positions with the expected vertically centered alignment, then verify the result in those same states.

Written by the indexing model from the issue text.