Revert "Issue #3069415 by bomoko, voleger: Call to deprecated method...

Revert "Issue #3069415 by bomoko, voleger: Call to deprecated method getSource() of class Drupal\twig_loader_test\Loader\TestLoader in core/modules/system/tests/modules/twig_loader_test/src/Loader/TestLoader.php on line 17"

This reverts commit dabe7a91.

core/modules/system/tests/modules/twig_loader_test/src/Loader/TestLoader.php

@@ -14,7 +14,7 @@ class TestLoader implements \Twig_LoaderInterface, \Twig_ExistsLoaderInterface,
    */
   public function getSourceContext($name) {
     $name = (string) $name;
-    $value = $name === 'kittens' ? 'kittens' : 'cats';
+    $value = $this->getSource($name);
     return new Source($value, $name);
   }
 
@@ -22,7 +22,12 @@ public function getSourceContext($name) {
    * {@inheritdoc}
    */
   public function getSource($name) {
-    return $this->getSourceContext($name)->getCode();
+    if ($name == 'kittens') {
+      return $name;
+    }
+    else {
+      return 'cats';
+    }
   }
 
   /**