minor #17812 [Yaml] always restore the error handler in tests (xabbuh)

This PR was merged into the 2.8 branch.

Discussion
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[Yaml] always restore the error handler in tests

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | https://github.com/symfony/symfony/pull/17809#discussion_r52928131
| License       | MIT
| Doc PR        |

The error handler must be restored even when assertions failed.

Commits
-------

7631202 [Yaml] always restore the error handler in tests

src/Symfony/Component/Yaml/Tests/ParserTest.php

@@ -896,10 +896,10 @@ EOF;
 
         $this->parser->parse($yaml);
 
+        restore_error_handler();
+
         $this->assertCount(1, $deprecations);
         $this->assertContains('Using a colon in the unquoted mapping value "bar: baz" in line 1 is deprecated since Symfony 2.8 and will throw a ParseException in 3.0.', $deprecations[0]);
-
-        restore_error_handler();
     }
 
     public function testColonInMappingValueExceptionNotTriggeredByColonInComment()