Fix IDE warnings of return when error

This fixes warnings generated by IDEs that element actions might return None in case of soft assert and later called with next actions.

Author: MartinsKMickus

testui/elements/testui_element.py

@@ -99,6 +99,7 @@ def __show_error(self, exception):
         :param exception: exception
         """
         testui_error(self.testui_driver, exception)
+        return self
 
     def get(self, index):
         """