[ChangesReporting] Fix total changed result on JsonOutputFormatter (#7807)

Author: samsonasik

src/ChangesReporting/Output/JsonOutputFormatter.php

@@ -27,7 +27,7 @@ public function report(ProcessResult $processResult, Configuration $configuratio
     {
         $errorsJson = [
             'totals' => [
-                'changed_files' => count($processResult->getFileDiffs()),
+                'changed_files' => $processResult->getTotalChanged(),
             ],
         ];