* Amend `.codecov.yml` to disable coverage reporting of test sources
and explicitly set most parameters
* Increase codecov upload retry time to 210s (from 35s)
* Upgrade gcovr adding support for more coverage formats (lcov, clover, jacoco)
* Upgrade github actions in coverage workflow
* Explicitly disable codecov plugins (also removing `gcov` coverage, which is not
correctly handled by codecov https://github.com/codecov/feedback/issues/334)