I18N: Add context to some plugin and theme strings for consistency.

Props ramiy, audrasjb.
Fixes #50710.

git-svn-id: https://develop.svn.wordpress.org/trunk@48520 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/theme.php

@@ -240,7 +240,7 @@ function get_theme_update_available( $theme ) {
 					sprintf(
 						'aria-label="%s" id="update-theme" data-slug="%s"',
 						/* translators: %s: Theme name. */
-						esc_attr( sprintf( __( 'Update %s now' ), $theme_name ) ),
+						esc_attr( sprintf( _x( 'Update %s now', 'theme' ), $theme_name ) ),
 						$stylesheet
 					)
 				);