reenable nsmap for root element

Makes it possible (again) to avoid the `kml:` prefix on every single tag
in the XML output.

Fixes: 84103d9 ("fix visibility and tests")
Fixes: 768a44c ("Refactor XML subelement handling in KML class")

fastkml/kml.py

@@ -85,11 +85,12 @@ def etree_element(
             root = config.etree.Element(f"{self.ns}kml")  # type: ignore[attr-defined]
             root.set("xmlns", config.KMLNS[1:-1])
         else:
-            try:
+            if hasattr(config.etree, "LXML_VERSION"):
                 root = config.etree.Element(  # type: ignore[attr-defined]
                     f"{self.ns}kml",
+                    nsmap={None: self.ns[1:-1]},
                 )
-            except TypeError:
+            else:
                 root = config.etree.Element(  # type: ignore[attr-defined]
                     f"{self.ns}kml",
                 )