minor #28673 [CS] Use combined assignment operators when possible (carusogabriel)

This PR was merged into the 2.8 branch.

Discussion
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[CS] Use combined assignment operators when possible

| Q             | A
| ------------- | ---
| Branch?       | 2.8
| Bug fix?      | no
| New feature?  | no <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | -   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | - <!-- required for new features -->

Less opcodes for us 😄

Commits
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c561e99394 [CS] Use combined assignment operators when possible

Author: nicolas-grekas

Input/InputDefinition.php

@@ -390,7 +390,7 @@ public function getSynopsis($short = false)
             if (!$argument->isRequired()) {
                 $element = '['.$element.']';
             } elseif ($argument->isArray()) {
-                $element = $element.' ('.$element.')';
+                $element .= ' ('.$element.')';
             }
 
             if ($argument->isArray()) {