I18N: Change context for the "Add New" string on Themes screen for consistency...

I18N: Change context for the "Add New" string on Themes screen for consistency with other similar strings.

Props ramiy.
Fixes #48875.
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git-svn-id: https://core.svn.wordpress.org/trunk@46612 1a063a9b-81f0-0310-95a4-ce76da25c4cd