MockMessageBar pushMessage method has incorrect signature

[couteau]

Describe the bug
MockMessageBar pushMessage method does not have the same signature as the actual QgsMessageBar pushMessage method

To Reproduce
Steps to reproduce the behavior:

1. Create a test plugin with a method that calls iface.messageBar().pushMessage('Test', Qgis.Warning) # without passing anything for the duration argument2.
2. Create a unit test that calls the plugin test method3.

Expected behavior
The unit test completes successfully

Environment (please complete the following information):

• OS: MacOS
• Python: 3.9
• Cookiecutter: n/a

Additional context
QgsMessageBar pushMessage has a default value for duration argument
MockMessageBar pushMessage does not causing unit tests if any code that relies on the default duration to crash
The signatures of the Mock class's pushMessage method and the real class's pushMessage method should be the same

[Joonalai]

Thank you for the issue. All the stub implementations should definitely be reviewed and updated to match the original classes.