We had a test failing several times in GitHub Actions where a user was
still logged in even after logout.
This issue can be reproduced running:
```
rspec spec/system/moderation/proposal_notifications_spec.rb:71 \
spec/system/notifications_spec.rb:126 --order defined
```
One possible cause is a concurrency issue because the process running
the test and the process running the browser both access the same
database connection. Maybe some database operations leak between tests
due to that, particularly if the previous test accessed the database
after starting the browser as well.
A way to avoid this possible cause is setting up the database before
starting the browser with a call to `visit`.
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