v0.0.29: [Coverage] Don't produce a JUnit report.
The `unittest` binary crashes with
```
unittest: /var/lib/gitlab-runner/builds/yS6csq8A/0/bigdata/mutable/mutable/third-party/catch2/include/catch2/catch.hpp:5918: virtual void Catch::CumulativeReporterBase<Catch::JunitReporter>::testCaseEnded(const Catch::TestCaseStats &) [DerivedT = Catch::JunitReporter]: Assertion `m_sectionStack.size() == 0' failed.
```
This error seems to be related to the Catch 2 JUnit reporter. See
https://github.com/catchorg/Catch2/issues/1801 and
https://github.com/catchorg/Catch2/issues/1967.
To remedy this problem, we simply don't use produce a report anymore.
It was never used, anyway.