minor symfony#18591 [Config] Fix XmlUtilsTest namespace (JhonnyL)

This PR was merged into the 2.3 branch.

Discussion
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[Config] Fix XmlUtilsTest namespace

| Q             | A
| ------------- | ---
| Branch?       | 2.3
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

Commits
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58425eb [Config] Fix XmlUtilsTest namespace

Author: stof

src/Symfony/Component/Config/Tests/Util/XmlUtilsTest.php

@@ -9,7 +9,7 @@
  * file that was distributed with this source code.
  */
 
-namespace Symfony\Component\Config\Tests\Loader;
+namespace Symfony\Component\Config\Tests\Util;
 
 use Symfony\Component\Config\Util\XmlUtils;