MDL-76415 portfolio: Fixed ${var} string interpolation deprecations.

Since PHP 8.2, placing the dollar sign outside the curly brace is deprecated when
the expression inside the braces resolves to a variable or an expression.

portfolio/googledocs/lib.php

@@ -99,7 +99,7 @@ public function send_package() {
             // Create each of the directories in Google Drive that we need.
             foreach ($directories as $directory) {
                 // Update the current path for this file.
-                $path .= "${directory}/";
+                $path .= "{$directory}/";
 
                 if (!isset($directoryids[$path])) {
                     // This directory hasn't been created yet so let's go ahead and create it.