Fix tests in test_get_forecasts.py

[nhoening]

After the extension to multiple providers, the tests there fail with the message: "Invalid provider name. Please set WEATHER_PROVIDER setting in config file to either OWM or WAPI, the two permissible options."

To reproduces, run pytest -k get_forecasts

See test failures in the pipeline here.

[devansh287]

Thank you so much for bringing this to my attention @nhoening! I have tried to address that in #9. Kindly review.