Submit both --all-features and --no-default--features coverage to codecov

[aborgna-q]

The extension_inference feature is experimental and may cause errors on otherwise correct code.
Hence we skip some tests when running with --all-features (see #795).
This means that those tests do not count for the coverage report sent to codecov.

To fix it we can submit both reports with/without extensions. Codecov then combines them into a single coverage metric.