Coding Standards: Use camel case with a lowercase first letter for the blockTheme array key.

This matches the WordPress JS naming conventions and the naming of other keys in the `$prepared_themes` array.

Follow-up to [52341].

See #54578, #53359.

git-svn-id: https://develop.svn.wordpress.org/trunk@52346 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/theme.php

@@ -782,7 +782,7 @@ function wp_prepare_themes_for_js( $themes = null ) {
 					? wp_nonce_url( admin_url( 'themes.php?action=' . $auto_update_action . '&stylesheet=' . $encoded_slug ), 'updates' )
 					: null,
 			),
-			'block_theme'    => $theme->is_block_theme(),
+			'blockTheme'     => $theme->is_block_theme(),
 		);
 	}