Fix kernel test to not depend on body field

Wolfgang Zieglerrequested to merge
issue/lupus_decoupled-3568705:3568705-automated-tests-fail into 1.x

The LupusDecoupledMenuRequestTest was extending LupusCeRendererKernelTestBase which uses node_add_body_field() - a function deprecated in Drupal 11.3. Since the body field storage is no longer provided by default, this caused "Attempt to create a field without a field_name" errors.

The menu test doesn't actually need any node/body functionality, so this change makes it extend KernelTestBase directly with only the modules needed for menu testing.

Closes #3568705

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