Why not mark them as flaky? Is there anything special to these two build configurations?

Only because I don't want to disable them for every build everywhere.

Ideally we introduce a way in the future to give us more qualifiers to "flaky". Like platforms, build combinations etc.

For this I introduced the ~ prefix for test numbers in runtests.pl. It does not disable them, but ignores the result in the CI status.

Also this seems to be the AppVeyor equivalent of #5954. Unfortunately I wasn't able to debug this RTSP test on Windows (yet).

Just mark this test as flaky-cmake

But its cmake-on-appveyor, or possibly cmake-on-win32. I think I rather stick to disabling it in appveyor for now.

Actually it is either not working due to MinGW, MSYS or Win32 since it is also broken for the autotools based builds on Azure Pipelines. So I don't think this is caused by CMake.

Short term, we can keep adding test numbers to ignore in the CI setup files, and then we can go over them all and see which are ignored where and see if we can draw conclusions and/or make better systems to handle them.