Dropdown buttons don't match height with sibling buttons in btn-group

The buttons don't have the same height within the button group. This currently affects whatever site is using the eclipsefdn_project_list shortcode.

Here are the known sites affected:

• https://webdev.eclipse.org/docs/hugo/components/eclipsefdn_projects/
• https://jakarta.ee/projects/

Relates to: https://github.com/jakartaee/jakarta.ee/issues/1588