Fix typo in DPNPBinaryFunc docstring

[antonwolfy]

The PR removes a duplicate word ("of of") in the DPNPBinaryFunc class docstring.

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[coveralls]

coverage: 78.092%. remained the same — fix-type-in-docstring into master

[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/index.html

[github-actions]

Array API standard conformance tests for dpnp=0.21.0dev1=py313h509198e_12 ran successfully.
Passed: 1355
Failed: 5
Skipped: 16