`test_buffers.py::test_device` was not actually checking the device of tensors

[rhaps0dy]

Description

I added a failure in case of unknown type to test_buffers.py::test_device, and made it iterate correctly through Tensors and dicts.

Motivation and Context

In test_buffers.py::test_device, the assertions that the device be the correct one would not be executed for RolloutBuffer and DictRolloutBuffer: the type of value is RolloutBufferSamples and DictRolloutBufferSamples respectively and so falls to the else case.

I have not raised an issue on purpose, why bother for a tiny bugfix.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Documentation (update in the documentation)

Checklist:

• [x] I've read the CONTRIBUTION guide (required)
• [x] I have updated the changelog accordingly (required).
• [ ] My change requires a change to the documentation.
• [x] I have updated the tests accordingly (required for a bug fix or a new feature).
• [ ] I have updated the documentation accordingly.
• [x] I have reformatted the code using make format (required)
• [x] I have checked the codestyle using make check-codestyle and make lint (required)
• [x] I have ensured make pytest and make type both pass. (required)
• [x] I have checked that the documentation builds using make doc (required)

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