Qutrit mixed test differentiability

[Gabriel-Bottrill]

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Context: Measuring and applying operation functionality have been added to the qutrit_mixed module, these tests ensure that these operations are differentiable. Description of the Change: Tests have been added that ensure that the apply_operation and measure functions retain differentiability for the new qutrit mixed-state device.

Benefits: Shows that the apply_operation and measure functions are differentiable.

Possible Drawbacks: N/A

Related GitHub Issues: N/A