fix tests

docs/notebooks/Site.ipynb

docs/notebooks/WindTurbines.ipynb

docs/notebooks/exercises/Validation.ipynb

py_wake/__init__.py

py_wake/site/wasp_grid_site.py

py_wake/site/xrsite.py

py_wake/tests/test_flow_map.py

py_wake/tests/test_sites/test_distances.py

py_wake/tests/test_sites/test_wasp_grid_site.py

py_wake/utils/grid_interpolator.py

py_wake/utils/xarray_utils.py

py_wake/wind_farm_models/wind_farm_model.py

py_wake/wind_turbines.py