Build/Test Tools: Properly transform theme.json files during copy.

The `theme.json` file `$schema` URL is relative in the `gutenberg` repository upstream. The URL is not currently being replaced with an aboslute one pointing to w.org due to a missing `transform: true` configuration.

Follow up to [61438], [61439], [61458], [61492], [61677].

See #64393.
Built from https://develop.svn.wordpress.org/trunk@61867


git-svn-id: http://core.svn.wordpress.org/trunk@61154 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/theme.json

@@ -1,5 +1,5 @@
 {
-	"$schema": "../schemas/json/theme.json",
+	"$schema": "https://schemas.wp.org/trunk/theme.json",
 	"version": 3,
 	"settings": {
 		"appearanceTools": false,

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '7.0-beta3-61866';
+$wp_version = '7.0-beta3-61867';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.