Fixed an issue in dpnp.random.vonmises function identified by running tests scope on PVC

[antonwolfy]

Function dpnp.isnan doesn't support scalar input and raises TypeError exception. But the call with scalar input is using by implementation of dpnp.random.vonmises function.

The PR proposes to always call numpy.isnan there instead, because it's secured that kappa is a scalar by a prior check in the code.

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[vlad-perevezentsev]

Thank you @antonwolfy