Fix parsing json backend cors

[robertop23]

I usually use the Python shell when I'm developing, but I cannot simple open it using the env vars because I get this error:

pydantic.env_settings.SettingsError: error parsing JSON for "BACKEND_CORS_ORIGINS"

How to reproduce this error:

cd backend/app/
export $(grep -v '^#' ../../.env | tr -d ' ' | xargs) && poetry run python

And inside the Python terminal:

from app.core.config import settings