Issue #3042848 by mikelutz: use ->load() instead of ->resolveTemplate in Twig Resolver tests

(cherry picked from commit b0a741c5)

core/modules/system/tests/src/Functional/Theme/TwigRegistryLoaderTest.php

@@ -41,7 +41,7 @@ public function assertTwigTemplate($value, $message = '', $group = 'Other') {
    * Tests template discovery using the Drupal theme registry.
    */
   public function testTemplateDiscovery() {
-    $this->assertTwigTemplate($this->twig->resolveTemplate('block.html.twig'), 'Found block.html.twig in block module.');
+    $this->assertTwigTemplate($this->twig->load('block.html.twig'), 'Found block.html.twig in block module.');
   }
 
   /**

core/modules/system/tests/src/Kernel/Theme/TwigNamespaceTest.php

@@ -42,10 +42,10 @@ public function assertTwigTemplate($value, $message = '', $group = 'Other') {
    */
   public function testTemplateDiscovery() {
     // Tests resolving namespaced templates in modules.
-    $this->assertTwigTemplate($this->twig->resolveTemplate('@node/node.html.twig'), 'Found node.html.twig in node module.');
+    $this->assertTwigTemplate($this->twig->load('@node/node.html.twig'), 'Found node.html.twig in node module.');
 
     // Tests resolving namespaced templates in themes.
-    $this->assertTwigTemplate($this->twig->resolveTemplate('@bartik/page.html.twig'), 'Found page.html.twig in Bartik theme.');
+    $this->assertTwigTemplate($this->twig->load('@bartik/page.html.twig'), 'Found page.html.twig in Bartik theme.');
   }
 
   /**