chore: heredoc indentation as of PHP 7.3

https://www.php.net/manual/en/language.types.string.php#language.types.string.syntax.heredoc

Author: keradus

Tests/Node/NodeTest.php

@@ -23,10 +23,10 @@ public function testToString()
         $node = new Node([new ConstantNode('foo')]);
 
         $this->assertEquals(<<<'EOF'
-Node(
-    ConstantNode(value: 'foo')
-)
-EOF
+            Node(
+                ConstantNode(value: 'foo')
+            )
+            EOF
             , (string) $node);
     }