Button focus should apply same colours as hover

Created by: sethjeffery

Fixes https://github.com/twbs/bootstrap/issues/21843

Since this change https://github.com/twbs/bootstrap/commit/a9bee8b6c8c31455dfba029434fad88b862c3846 buttons rendered with <a> have been inheriting their focus colour from reboot instead of overriding it with the button style.

Before

After