Playing around with the test to find the error.

tests/src/Kernel/EntityViewBuilderTest.php

@@ -92,7 +92,7 @@ final class EntityViewBuilderTest extends AbstractTestCase {
       </article>
     HTML;
     $actual_html = $this->renderPlain($build);
-    self::assertSame(htmlspecialchars(self::normalizeHtml($expected_html)), htmlspecialchars(self::normalizeHtml($actual_html)));
+    self::assertSame((string)$expected_html)), (string)$actual_html));
 
     // -- Teaser mode.
     $build = $view_builder->build($public_node, 'teaser');