Tweak format to be easier to copy-paste-and-tweak to theme.json

"file:./" URLs are relative to the theme's root because a theme.json file is always in the root of the theme. The "file:./" syntax is consistent with the way styles/scripts are defined in a block.json file for blocks.

functions.php

@@ -26,15 +26,15 @@ function twentytwentytwo_support() {
 				'fontWeight'  => '200 900',
 				'fontStyle'   => 'normal',
 				'fontStretch' => 'normal',
-				'src'         => get_theme_file_uri( 'assets/fonts/source-serif-pro/SourceSerif4Variable-Roman.ttf.woff2' ),
+				'src'         => 'file:./assets/fonts/source-serif-pro/SourceSerif4Variable-Roman.ttf.woff2',
 				'provider'    => 'local',
 			),
 			array(
 				'fontFamily'  => 'Source Serif Pro',
 				'fontWeight'  => '200 900',
 				'fontStyle'   => 'italic',
 				'fontStretch' => 'normal',
-				'src'         => get_theme_file_uri( 'assets/fonts/source-serif-pro/SourceSerif4Variable-Italic.ttf.woff2' ),
+				'src'         => 'file:./assets/fonts/source-serif-pro/SourceSerif4Variable-Italic.ttf.woff2',
 				'provider'    => 'local',
 			),
 		)