Add proper handling of unput array of `usm_ndarray` type in `dpnp.ix_`

[antonwolfy]

The PR is intended to resolve an exception raised while passing input array of usm_ndarray type. The test is added to cover the scenario. Also small improvements to existing tests are implemented.

• [x] Have you provided a meaningful PR description?
• [x] Have you added a test, reproducer or referred to issue with a reproducer?
• [x] Have you tested your changes locally for CPU and GPU devices?
• [x] Have you made sure that new changes do not introduce compiler warnings?
• [ ] Have you checked performance impact of proposed changes?
• [ ] If this PR is a work in progress, are you filing the PR as a draft?

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