minor #27757 [Validator] Fix the namespace of RegexTest (dunglas)

This PR was merged into the 2.8 branch.

Discussion
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[Validator] Fix the namespace of RegexTest

| Q             | A
| ------------- | ---
| Branch?       | 2.8
| Bug fix?      | no
| New feature?  | no <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | n/a  <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | n/a <!-- required for new features -->

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Commits
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fe7fc44 [Validator] Fix the namespace of RegexTest

src/Symfony/Component/Validator/Tests/Constraints/RegexTest.php

@@ -9,7 +9,7 @@
  * file that was distributed with this source code.
  */
 
-namespace Constraints;
+namespace Symfony\Component\Validator\Tests\Constraints;
 
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Validator\Constraints\Regex;