Reenable codecov integration #8394
Description
Lately I've seen a couple of bug fixes of obvious code issues like #8392.
A while ago codecov was disabled in this repository in light of its security incident but I think it is appropriate to reenable it as the CI has been migrated to GHA which has a lower vulnerability surface than Circle did (the step will only have secrets passed explicitly). Or even more strict would be to only enable for PRs but not for main branch to ensure 100% that no secrets can be leaked. It's currently very hard to ensure good code coverage when reviewing PRs, nor should it be a manual process like that but should be assisted by a tool like codecov.