In lxml 5.1.1 the private name `_ElementStringResult` in module `lxml.etree`
does no longer exists.
This code was written nearly a decade ago, its no longer clear what the
intention `_ElementStringResult` and `_ElementUnicodeResult` had been. It can be
assumed that these classes will no longer occur.
Closes: https://github.com/searxng/searxng/issues/3368
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>