fix: fixed DeprecationWarning from pytest about `np.int`.

[JSLJ23]

Fixed DeprecationWarning from pytest about np.int.

• 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 self._voxels = np.ceil(np.array(box_size) / self._spacing).astype(np.int)

Changed np.int to np.int32 in line 260 of vina.py.

[markllama]

This would be better served by PR #167