[Yaml] always restore the error handler in tests

The error handler must be restored even when assertions failed.

Author: xabbuh

Tests/ParserTest.php

@@ -896,10 +896,10 @@ public function testColonInMappingValueException()
 
         $this->parser->parse($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()