Add appropriate text to an exception

Author: abstractedfox

Lib/xml/etree/ElementTree.py

@@ -546,7 +546,8 @@ def _setroot(self, element):
 
         """
         if not iselement(element):
-            raise TypeError
+            raise TypeError(f"element must be etree.Element, "
+                            f"not {type(element).__name__}")
         self._root = element
 
     def parse(self, source, parser=None):