Use license_files instead of license_file in setup.cfg [metadata] section.
When using license_file, setuptools prints a warning: “setuptools._deprecation_warning.SetuptoolsDeprecationWarning: The license_file parameter is deprecated, use license_files instead.”.
The license_files key was introduced in “wheel” package Git commit 59976ab294e1b118f42cab404d95df66ed55f7e4 from 2018-07-16. The disadvantage of this change is that when using wheel < 0.32.0, the resulting wheel will not contain the license file in its .dist-info directory.