Applications may crash.
If a crash happens on a remote system during CI run it's sometimes very hard to understand the reason. The most important means to analyze such is a stack trace.

It's also very important to check whether there was a core dump or not, even a test passed.
For example, in my personal runner, all tests passed, but ns-slapd crashed during that time:
https://dev.azure.com/slev0400/slev/_build/results?buildId=1382&view=logs&j=d3570036-a909-5cd9-6fb1-2aa40c0554fe

For Docker environment, the core dumps are collected by the host's systemd-coredump,
which knows nothing about such containers (for now). To build an informative thread stack trace debuginfo packages should be installed. But they can't be installed on the host OS (ubuntu), That's why after all the tests completed an additional container should be up and the host's core dumps and host's journal should be passed into it.

Even if there weren't enough debuginfo packages at CI-runtime, the core dump could be analyzed locally later.