Search: Fix attribute defaults (#23777)

* Search: Fix attribute defaults

Prior to d26842b, the Search block's label and buttonText attributes
defaulted to `__( 'Search' )`. This meant that adding a Search block to
a post or page resulted in `<!-- wp:search /-->` being inserted into the
HTML.

In d26842b, the defaults were removed so that Search could use a
block.json file. The default values were instead implemented using a
default block variation.

This, however, meant that Search blocks added prior to d26842b would
render with a blank label and button.

This fix is to default label and buttonText to `__( 'Search' )` in the
render_callback. Care must be taken here to permit these attributes to
be '' in which case the label and/or button are hidden.

* Try to trick GitHub into re-running tests

packages/block-library/src/search/index.php

@@ -15,6 +15,18 @@
 function render_block_core_search( $attributes ) {
 	static $instance_id = 0;
 
+	// Older versions of the Search block defaulted the label and buttonText
+	// attributes to `__( 'Search' )` meaning that many posts contain `<!--
+	// wp:search /-->`. Support these by defaulting an undefined label and
+	// buttonText to `__( 'Search' )`.
+	$attributes = wp_parse_args(
+		$attributes,
+		array(
+			'label'      => __( 'Search' ),
+			'buttonText' => __( 'Search' ),
+		)
+	);
+
 	$input_id      = 'wp-block-search__input-' . ++$instance_id;
 	$label_markup  = '';
 	$button_markup = '';