Fix package discovery in pyproject .toml

[avalentino]

The current content of the xarray-eopf wheel in PyPI is

xarray_eopf-0.2.7-py3-none-any
├── integration
├── tests
├── xarray_eopf
└── xarray_eopf-0.2.7.dist-info

This path fixes the setuptools package discovery configuration to include only the xarray-eopf package and sub-packages.

[konstntokas]

Thank you for the fix - approved :)