minor #14121 CS: Pre incrementation/decrementation should be used if possible (gharlan)

This PR was merged into the 2.3 branch.

Discussion
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CS: Pre incrementation/decrementation should be used if possible

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

Fixes provided by new fixer: PHP-CS-Fixer/PHP-CS-Fixer#1113

If this pr is merged I would change the level of the fixer to `symfony`.

Commits
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c5123d6 CS: Pre incrementation/decrementation should be used if possible

Author: fabpot

Loader/FileLoader.php

@@ -91,7 +91,7 @@ public function import($resource, $type = null, $ignoreErrors = false, $sourceRe
             }
 
             $resources = is_array($resource) ? $resource : array($resource);
-            for ($i = 0; $i < $resourcesCount = count($resources); $i++) {
+            for ($i = 0; $i < $resourcesCount = count($resources); ++$i) {
                 if (isset(self::$loading[$resources[$i]])) {
                     if ($i == $resourcesCount - 1) {
                         throw new FileLoaderImportCircularReferenceException(array_keys(self::$loading));