I guess our source space morphing example uses too much memory (?) because for example:

https://app.circleci.com/pipelines/github/mne-tools/mne-python/4060/workflows/c908299a-3a9e-4e92-9f6b-e09f9ce33fc4/jobs/22741

It doesn't look too bad here:

https://mne.tools/dev/auto_examples/forward/sg_execution_times.html

So it's also possible it's whatever example immediately follows that one.