minor #13645 fixed possible race condition when creating a directory (fabpot)

This PR was merged into the 2.3 branch.

Discussion
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fixed possible race condition when creating a directory

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #13228
| License       | MIT
| Doc PR        | n/a

Commits
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8542866 fixed possible race condition when creating a directory

Author: fabpot

DependencyInjection/FrameworkExtension.php

@@ -666,7 +666,7 @@ private function registerAnnotationsConfiguration(array $config, ContainerBuilde
 
         if ('file' === $config['cache']) {
             $cacheDir = $container->getParameterBag()->resolveValue($config['file_cache_dir']);
-            if (!is_dir($cacheDir) && false === @mkdir($cacheDir, 0777, true)) {
+            if (!is_dir($cacheDir) && false === @mkdir($cacheDir, 0777, true) && !is_dir($cacheDir)) {
                 throw new \RuntimeException(sprintf('Could not create cache directory "%s".', $cacheDir));
             }