Stop calling parent::sendHeaders() in sendContent()

Closes #3511983

src/Response/QRImageResponse.php

@@ -107,7 +107,7 @@ class QRImageResponse extends Response {
    */
   public function sendContent(): static {
     $this->generateQrCode($this->data);
-    return parent::sendHeaders();
+    return parent::sendContent();
   }
 
   /**