raise an error when the configuration from EWOKS_CONFIG_URI is empty

[woutdenolf]

We were struggling yesterday with the celery configuration because this is not a syntax error in python (type annotations):

broker_url: f"sqla+sqlite:///celery.db"
result_backend: f"db+sqlite:///celery_results.db"

Solution: raise when config has no global variables.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/ewoksjob/config.py	50.00%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[woutdenolf]

CI needed fixing as well. It was reported upstream: redis/redis-om-python#833.

[woutdenolf]

I merge. I need the fix in the CI.