Install: Prevent DB errors caused by web fonts API.

Bypass checking `theme.json` for web fonts during the installation of WordPress.

During installation the active theme is considered to be Twenty Twenty-Two (the default theme). As a block theme this prompts a database call when the web fonts API checks the `theme.json` settings, this triggers a database error during installation as the database tables do not exist.

Props chouby, costdev, peterwilsoncc, sergeybiryukov.
Fixes #55632.



git-svn-id: https://develop.svn.wordpress.org/trunk@53306 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/script-loader.php

@@ -3057,6 +3057,11 @@ function wp_enqueue_block_style( $block_name, $args ) {
  * @access private
  */
 function _wp_theme_json_webfonts_handler() {
+	// Block themes are unavailable during installation.
+	if ( wp_installing() ) {
+		return;
+	}
+
 	// Webfonts to be processed.
 	$registered_webfonts = array();