Bundled Themes: Twenty Twenty property border-style is overwritten - coding standard.

Fixes coding standard violations in the classic editor stylesheets.

Props ankitmaru.
Fixes #49006.
Built from https://develop.svn.wordpress.org/trunk@47264


git-svn-id: https://core.svn.wordpress.org/trunk@47064 1a063a9b-81f0-0310-95a4-ce76da25c4cd