Upgrade codecov to _not_ use the bash uploader anymore

Codecov has announced the EOL for their uploader, known as the bashuploader. We currently use the codecov orb of circleci that still uses the bash uploader.

I had tried simply bumping the version of the orb in #5452.

This resulted in _no_ coverage being uploaded. The coverage of ~ 50% reported was manually done by first invoking `gcov` on all `gcno` files and then invoking `./codecov` all within an ssh session on CircleCI.

Blog for deprecation of the bash uploader: https://about.codecov.io/blog/codecov-uploader-deprecation-plan/

This needs to be executed before Feb 1st 2022, as the bash uploader will completely be sunset at that date.
From now on we can expect sporadic brownouts of the bash uploader. This could be observed as the coverage jobs failing on CI. This will probably not result in test failures, however, it could show as 0% coverage, or a significant drop in coverage on PR's.