This updates `autoprefixer` from version `9.6.2` to `9.8.6`. This includes changes as a result of running `npm run grunt precommit:css`. See #51801. Built from https://develop.svn.wordpress.org/trunk@50017 git-svn-id: http://core.svn.wordpress.org/trunk@49718 1a063a9b-81f0-0310-95a4-ce76da25c4cd