SimpleTestCase._remove_databases_failures() is not idempotent and crashes on complex MRO.

[Michele Fiori]

When using complex test inheritance (e.g., mixing multiple LiveServerTestCase subclasses or dynamic test class generation), the cleanup method
_remove_databases_failures can be called in a state where database connection methods have already been unwrapped or were never wrapped for a specific alias.

Currently, the code assumes the wrapped attribute always exists: setattr(connection, name, method.wrapped)

This leads to an AttributeError: 'function' object has no attribute 'wrapped'.

The proposed fix adds a defensive hasattr(method, "wrapped") check to make the teardown process idempotent and robust against complex class hierarchies.

PR: ​https://github.com/django/django/pull/20758