CI(pytest): Upload test results to Codecov for test analytics

[echoix]

Codecov had this feature announced and available for a while now, but they're pushing it a little more now. I think it can be useful a bit.

Basically, you can upload a junit-style xml test report, which basically is an xml file with the test names, the results, and the time taken. Pytest works out of the box. The goal is to upload even on test failures, so that we can analyze which tests are flaky, how many are failing often etc.

For unittest, there's a package that we could use that replaces unittest' test runner class, but gunittest already does the same thing, so it's not readily available yet to implement (it would be more useful to get a value on the i.smap failure rate for example).

I was waiting before working on this and submitting a PR as it wasn't clear if the pull request comments would be posted on failures. There has been some feedback since, and I didn't see one yet, even if I did a PR with purposely failing tests after merging in my main branch (adding/removing "not" in asserts).

The interface, for the main branch (of my fork, play with it at https://app.codecov.io/gh/echoix/grass/tests/main), looks like:

I configured flags, so we can filter them:

It also analyzes what are the slow tests. For example, in our pytest tests, 28 tests take way more time than the others. (The time seems like for the last 30 days, but less since it's been on my main branch for only a couple commits, at the first commit it was like 4-5 minutes for a subset of 23 tests)

Here's an example for a branch, and also showing where there's a flaky test (a new v.class test from #6071, on sometimes fails on Windows, even in the main repo):

I didn't try on my second fork to see how it behaves without a codecov token. I strongly suppose it works the same as for code coverage upload, which still worked yesterday. Technically, they shouldn't have made a separate action, as it is pretty much the same as the code coverage upload action, it even uses the same cli binary uploader.

There was a beta feature in oct 2023 that looks still in beta that used a similar mechanism. You uploaded a list of tests collected before actually running them, and from the code coverage, the labels, the flags, and the changes, it would select the tests that must be ran, maybe a bit more, and you run these. I don't feel it was appropriate or ready to rely on, but it was an interesting idea. Having only the test results uploaded doesn't have any real impact if it stops working.

I also tried out using open id connect (oidc) with the use_oidc: true + adding workflow permissions instead of having the CODECOV_TOKEN, for both the test result upload and code coverage upload, and both worked fine multiple times. I simply kept it out fromm here, as it was not needed to work correctly.

[echoix]

I forgot to cherry-pick a commit that avoids uploading xml files from the gui/ folder, as they are useless for analyzing the test results