Views Tables - Use usa-table--sticky-header

USWDS 3.8.0 introduced the CSS class 'usa-table--sticky-header'. views-view-table.html.twig adds the class 'sticky-enabled' if the sticky headers have been enabled for the table.

Add 'usa-table--sticky-header' class if sticky headers have been enabled for the view table.

Probably wise to still add 'sticky-enabled' for backward-compatibility with projects that use that class.