minor #20505 [DOMCrawler] Bug fixed (Imangazaliev)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes #20505).

Discussion
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[DOMCrawler] Bug fixed

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT
| Doc PR        | reference to the documentation PR, if any

Commits
-------

6c3150d [DOMCrawler] Bug fixed

src/Symfony/Component/DomCrawler/Crawler.php

@@ -816,7 +816,7 @@ class Crawler extends \SplObjectStorage
             }
         }
 
-        return sprintf('concat(%s)', implode($parts, ', '));
+        return sprintf('concat(%s)', implode(', ', $parts));
     }
 
     /**