Venv deadlock in CI tests

[phil-opp]

We often get venv deadlocks in our CI. The result is that jobs hang at "Waiting to acquire lock for /home/runner/work/dora/dora/.venv at /home/runner/work/dora/dora/.venv/.lock".

These errors are spurious and often disappear when rerunning the job. But it is still very annoying, so we should fix this.

[phil-opp]

@haixuanTao Do you have any idea what could cause this? I don't have much experience with venvs, so my attempts to debug this were not successful.

[haixuanTao]

I have no idea.