Themes: Revert one instance of wp_get_theme() from [54817].

Since this specific call to `wp_get_theme()` is found within `wp-includes/blocks`, this change will need to be made upstream in the Gutenberg repository.

See #57057.
Built from https://develop.svn.wordpress.org/trunk@54819


git-svn-id: http://core.svn.wordpress.org/trunk@54371 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/blocks/template-part.php

@@ -22,7 +22,7 @@ function render_block_core_template_part( $attributes ) {
 	if (
 		isset( $attributes['slug'] ) &&
 		isset( $attributes['theme'] ) &&
-		get_stylesheet() === $attributes['theme']
+		wp_get_theme()->get_stylesheet() === $attributes['theme']
 	) {
 		$template_part_id    = $attributes['theme'] . '//' . $attributes['slug'];
 		$template_part_query = new WP_Query(