[python-package] fix mypy error about ctypes array creation

[jameslamb]

Contributes to #3756
Contributes to #3867.

Fixes the following mypy.

python-package/lightgbm/basic.py:315: error: "int" not callable  [operator]
python-package/lightgbm/basic.py:315: error: Unsupported operand types for * ("type" and "int")  [operator]

Notes for Reviewers

Using the * operator is the expected way to create a C array using ctypes, but mypy is confused about it.

Docs: https://docs.python.org/3/library/ctypes.html#arrays

This is a frequently-run code path covered by lots of tests, so I think just ignoring this warning from mypy is safe.

[github-actions]

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