minor #34625 [HttpKernel] reset the kernel cache after each test (xabbuh)

This PR was merged into the 4.4 branch.

Discussion
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[HttpKernel] reset the kernel cache after each test

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       |
| License       | MIT
| Doc PR        |

Commits
-------

5b5927b93b reset the kernel cache after each test

src/Symfony/Component/HttpKernel/Tests/KernelTest.php

@@ -30,7 +30,7 @@ use Symfony\Component\HttpKernel\Tests\Fixtures\ResettableService;
 
 class KernelTest extends TestCase
 {
-    public static function tearDownAfterClass(): void
+    protected function tearDown(): void
     {
         $fs = new Filesystem();
         $fs->remove(__DIR__.'/Fixtures/var');