codecov does not include submodule code in the report or statistics

[joanise]

Relevant codecov.io threads:

• https://community.codecov.com/t/codecov-io-ui-not-resolving-submodule-paths-in-github/713
• https://community.codecov.com/t/problem-getting-the-source-code-from-your-provider-unable-to-show-line-by-line-coverage/4128
• https://community.codecov.com/t/coverage-of-external-files/1315

I have tried some variants in branch dev.ej/codecov-with-submodules to attempt to fix this, but no luck.

When I expect the payload uploaded to codecov, I can see that the submodule code is in the XML part of the payload, but the file list at the beginning does not include the submodule python files, which is probably why they're excluded. I've inspected the code in our upload action, https://github.com/codecov/codecov-action but I didn't find where the file list is being built or how to trigger the change we need.