Select group label renders above option items when virtualScroller is enabled

[m-prang]

When using the select component with grouped options and virtualScroll, group labels with long text content wrap onto multiple lines and render above the option items.

Reproduction:
StackBlitz: https://stackblitz.com/edit/4tftrehq-9zi7sdja

Steps to reproduce:

1. Use a select with group=true
2. Enable virtualScroll and set a virtualScrollItemSize
3. Create options and include group label with a long string
4. Run and open the dropdown

Expected Behavior:
Behaves the same as long string in select options and remain on single line. Horizontal scrolling should occur if needed.

PrimeUIX:
2.0.2

Possible Fix:
Add the style white-space: nowrap for the class .p-select-option-group-label