Disable code coverage in CI

[konnov]

Removing test-coverage from the CI workflows:

• It slows down the build times
• scoverage is not up-to-date, see this build
• I don't think anybody was looking at the coverage plots in years.

Without code coverage in tests:

With code coverage in tests:

The integration tests are still slower though, so the total build times are not changing.

[konnov]

I will merge this one, to see whether it unlocks other PRs. If you have objections, we can come back to this later.