gh-131938: Update exception message for Element.remove() when an element is not found (#131972)

The exception message for `xml.etree.ElementTree.Element.remove` when an element is not found
has been updated from "list.remove(x): x not in list" to "Element.remove(x): element not found".

Modules/_elementtree.c

@@ -1654,7 +1654,8 @@ _elementtree_Element_remove_impl(ElementObject *self, PyObject *subelement)
     }
 
     if (rc == 0) {
-        PyErr_SetString(PyExc_ValueError, "list.remove(x): x not in list");
+        PyErr_SetString(PyExc_ValueError,
+                        "Element.remove(x): element not found");
         return NULL;
     }