[tests] fix deprecation numpy warning

[StrikerRUS]

  /__w/1/s/tests/python_package_test/test_basic.py:173: DeprecationWarning: `np.int` is a deprecated alias for the builtin `int`. To silence this warning, use `int` by itself. Doing this will not modify any behavior and is safe. When replacing `np.int`, you may wish to use e.g. `np.int64` or `np.int32` to specify the precision. If you wish to review your current use, check the release note link for additional information.
  Deprecated in NumPy 1.20; for more details and guidance: https://numpy.org/devdocs/release/1.20.0-notes.html#deprecations

[jameslamb]

Looks great, thanks! I checked for other instances of the deprecated aliases mentioned at https://numpy.org/devdocs/release/1.20.0-notes.html#deprecations with git grep but couldn't find any.

[github-actions]

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