Change argument type for xml.etree.ElementTree.iselement() to object (#2642)

It should be possible to ask for every object whether it looks like
an element. If only Elements are accepted, this function would always
return True.

Fixes #2629

Author: mthuurne

stdlib/2and3/xml/etree/ElementTree.pyi

@@ -8,7 +8,7 @@ VERSION = ...  # type: str
 
 class ParseError(SyntaxError): ...
 
-def iselement(element: Element) -> bool: ...
+def iselement(element: object) -> bool: ...
 
 _T = TypeVar('_T')