Dashboard: Do not show "Search Engines Discouraged" text when the `blog_public` option is not set.

Search engines are only discouraged from indexing the site when the option is explicitly set to `0`.

Fixes #34860.
Built from https://develop.svn.wordpress.org/trunk@35873


git-svn-id: https://core.svn.wordpress.org/trunk@35837 1a063a9b-81f0-0310-95a4-ce76da25c4cd