[TODO] Fix coverage collection for Cython modules

[webknjaz]

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Describe the bug

Some time between https://app.codecov.io/gh/aio-libs/yarl/commit/d1286dbe71ea1caaf7c8e488b608ae1637702e90 (d1286db) and https://app.codecov.io/gh/aio-libs/yarl/commit/63c446174218bdcd31274b4488e513de1a05c54e (63c4461) Codecov forgot about the existance of Cython modules entirely.
Need to bisect that and see what happened.

To Reproduce

🤷‍♂️

Expected behavior

*.pyx files should show coverage.

Additional context

The same thing is happening in another project with identical setup: ansible/pylibssh#781.

The only thing suspicious in the diff is the changes to the linetrace setting: d1286db...63c4461. However, ansible-pylibssh still has this setting on and has this problem nevertheless. So I think this might be unreleated.

My guess is that perhaps Cython was unpinned at the time and we didn't notice when this changed.

[webknjaz]

I compared the uploads before and after, and both have the .pyx file in the file list at the beginning of the payload but the XML portion only has mention of the .pyx file in the older one.

This likely means that coveragepy does not collect coverage data for the Cython module. This might be caused by one of coveragepy, Cython plugin or Cython itself.