[fix] Bing-WEB: use <span class='algoSlug_icon'> for the description

On some result items from Bing-WEB the `<span class='algoSlug_icon'>` tag is the
only tag that contains a description.  The issue can be reproduced by [1]::

    !bi vmware

[1] https://github.com/searxng/searxng/issues/1764#issuecomment-1417990531



Reported-by: @AlyoshaVasilieva
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>