Accessibility: Site Health: Make the heading text for site health check issues...

Accessibility: Site Health: Make the heading text for site health check issues easier to select in Firefox.

Props afercia, sabernhardt, johnbillion, Clorith, audrasjb.
Fixes #50281.
Built from https://develop.svn.wordpress.org/trunk@48144


git-svn-id: https://core.svn.wordpress.org/trunk@47913 1a063a9b-81f0-0310-95a4-ce76da25c4cd