Bundled Themes: Twenty Seventeen CSS issue when using rowspan in tables.

Fixes CSS issue when using rowspan in tables. This issue does not apply to the Table Block, just tables inserted as custom html.

Props aussi, subrataemfluence, jainnidhi.
Fixes #44004.
Built from https://develop.svn.wordpress.org/trunk@48028


git-svn-id: https://core.svn.wordpress.org/trunk@47796 1a063a9b-81f0-0310-95a4-ce76da25c4cd