Help tabs: Update media help text to reflect 4.0.

fixes #28654.

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4.0-RC1.

Built from https://develop.svn.wordpress.org/trunk@29647


git-svn-id: http://core.svn.wordpress.org/trunk@29421 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Correct a Sass typo that somehow slipped by in [29616].

see #28267.

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git-svn-id: http://core.svn.wordpress.org/trunk@29422 1a063a9b-81f0-0310-95a4-ce76da25c4cd