Objects with __toString magic method are valid string-typed values

```
{% set foo %}Hello{% endset %}
{% types {foo: 'string'} %}
```
Actually, `$context['foo'] instanceof Twig\Markup`.

composer.json

@@ -8,7 +8,7 @@
             "name": "Jeroen Versteeg"
         }
     ],
-    "version": "1.0.7",
+    "version": "1.0.8",
     "autoload": {
         "psr-4": {
             "AlisQI\\TwigQI\\": "src/"

src/Assertion/AssertType.php

@@ -27,7 +27,7 @@ public static function matches($value, string $type): bool
         }
 
         return match ($type) {
-            'string' => is_string($value),
+            'string' => is_string($value) || (is_object($value) && method_exists($value, '__toString')),
             'number' => is_int($value) || is_float($value),
             'boolean' => is_bool($value),
             'iterable' => is_iterable($value),

tests/TypeAssertionsTest.php

@@ -5,7 +5,9 @@
 namespace AlisQI\TwigQI\Tests;
 
 use ArrayIterator;
+use DateTime;
 use Exception;
+use Twig\Markup;
 use Twig\Node\Node;
 
 class TypeAssertionsTest extends AbstractTestCase
@@ -74,11 +76,13 @@ public static function getTypes(): array
             ['string', 'hello', true],
             ['string', '', true],
             ['string', '0', true],
+            ['string', new Markup('hello', 'UTF-8'), true], // class Markup implements \Stringable
+            ['string', new Exception(), true], // Exception has __toString()
 
             ['string', true, false],
             ['string', 1, false],
             ['string', [], false],
-            ['string', new Exception(), false],
+            ['string', new DateTime(), false],
 
             ['number', 0, true],
             ['number', 1, true],