This update fixes an issue where tests were being run twice due to improper test class inheritance. The fix reorganizes the test structure to use a shared common test case and properly creates necessary test data, eliminating the duplicate test runs. This improves testing efficiency and reduces unnecessary processing time.

When inheriting from a test case that contains tests methods, the tests are run twice. The only reason to inherit from this case here, was to use the created partner.

So let's use the existing common case ans let's create the partner.

Forward-Port-Of: odoo/enterprise#54727