Add fixture for implicit readonly property promotion on DowngradeReadonlyPropertyRector (#315)

Author: samsonasik

rules-tests/DowngradePhp81/Rector/Property/DowngradeReadonlyPropertyRector/Fixture/readonly_implicit_property_promotion.php.inc

@@ -0,0 +1,29 @@
+<?php
+
+namespace Rector\Tests\DowngradePhp81\Rector\Property\DowngradeReadonlyPropertyRector\Fixture;
+
+class ReadonlyImplicitPropertyPromotion
+{
+    public function __construct(
+        readonly string $foo = 'foo'
+    )
+    {
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\Tests\DowngradePhp81\Rector\Property\DowngradeReadonlyPropertyRector\Fixture;
+
+class ReadonlyImplicitPropertyPromotion
+{
+    public function __construct(
+        public string $foo = 'foo'
+    )
+    {
+    }
+}
+
+?>