htmllaundry: if link_target is a list, use only the first item.

And it *must* be a list with lxml 5.2 (new lxml_html_cleaner package), otherwise you get an error when instantiating the cleaner:

```
TypeError: Expected a collection, got str: link_target='_blank'
```

src/euphorie/htmllaundry/cleaners.py

@@ -4,7 +4,7 @@
 try:
     from lxml_html_clean.clean import _find_external_links
 except ImportError:
-    # lxml 4, Plone 6.0.10 or earlier
+    # lxml 5.1 or earlier, Plone 6.0.10 or earlier
     from lxml.html.clean import _find_external_links
 
 
@@ -24,6 +24,8 @@ def force_link_target(self, doc, target):
             if target is None:
                 if "target" in el.attrib:
                     del el.attrib["target"]
+            elif isinstance(target, (list, tuple)):
+                el.set("target", target[0])
             else:
                 el.set("target", target)