This commit replaces the use of EngineTestKit to test scenarios where
bean override could not process the test class. There is no need to
run an actual test for this as:
1. Regular integration tests are already validating that adding the
annotation triggers the processing as part of executing the test.
2. The entry point is a ContextCustomizer that can easily be invoked
in a regular test.
As part of harmonizing this, AbstractTestBeanIntegrationTestCase can
be nested, and BeanOverrideTestSuite serve no purpose. The tests can
be executed in an IDE without any special setup.
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