[VarExporter] Fix exporting enums

Author: nicolas-grekas

Internal/Exporter.php

@@ -198,7 +198,7 @@ public static function export($value, string $indent = '')
             case true === $value: return 'true';
             case null === $value: return 'null';
             case '' === $value: return "''";
-            case $value instanceof \UnitEnum: return ltrim(var_export($value, true), '\\');
+            case $value instanceof \UnitEnum: return '\\'.ltrim(var_export($value, true), '\\');
         }
 
         if ($value instanceof Reference) {

Tests/Fixtures/unit-enum.php

@@ -1,5 +1,5 @@
 <?php
 
 return [
-    Symfony\Component\VarExporter\Tests\Fixtures\FooUnitEnum::Bar,
+    \Symfony\Component\VarExporter\Tests\Fixtures\FooUnitEnum::Bar,
 ];