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: https://github.com/FriendsOfPHP/PHP-CS-Fixer/pull/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

ClassMapGenerator.php

@@ -95,7 +95,7 @@ class ClassMapGenerator
         $classes = array();
 
         $namespace = '';
-        for ($i = 0, $max = count($tokens); $i < $max; $i++) {
+        for ($i = 0, $max = count($tokens); $i < $max; ++$i) {
             $token = $tokens[$i];
 
             if (is_string($token)) {