Make tempfile path unique

The temp-file that the test currently creates is `/tmp/log`.
This may exist on many platforms already (including `platform.sh` app containers).
With the proposed patch way the collision will be less likely.

Sponsored-by: Platform.sh

src/Symfony/Component/HttpKernel/Tests/Log/LoggerTest.php

@@ -34,7 +34,7 @@ class LoggerTest extends TestCase
 
     protected function setUp()
     {
-        $this->tmpFile = sys_get_temp_dir().\DIRECTORY_SEPARATOR.'log';
+        $this->tmpFile = tempnam(sys_get_temp_dir(), 'log');
         $this->logger = new Logger(LogLevel::DEBUG, $this->tmpFile);
     }