mind file uploads in nested array keys (#18276)

Author: themsaid

src/Illuminate/Foundation/Testing/Concerns/MakesHttpRequests.php

@@ -304,6 +304,10 @@ protected function extractFilesFromDataArray(&$data)
 
                 unset($data[$key]);
             }
+
+            if (is_array($value)) {
+                $files[$key] = $this->extractFilesFromDataArray($value);
+            }
         }
 
         return $files;