[Tile] Update the border on Expandable with interactive tiles

[thyhmdo]

Storybook link: https://react.carbondesignsystem.com/?path=/story/experimental-feature-flags-tile--expandable-with-interactive

Since the entire tile is not clickable, the border should be around the button instead of being around the tile

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[tay1orjones]

This should be a pretty simple style-only change for the ExpandableTile with interactive elements