Joplin _test_incremental_builds no longer works

## Describe the bug
When we run our incremental build tests (base/tests/_test_incremental_builds.py), they don't work anymore. We get 3 errors. This is possibly due to the fact that they use data directly from mutable production datadumps.

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## To Reproduce
Steps to reproduce the behavior
example:
1. pipenv run python joplin/manage.py test _test_incremental_builds
2. See errors

## Current behavior
A clear and concise description of what happened

## Expected behavior
A clear and concise description of what you expected to happen

## Screenshots

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## Additional context
If you generate explicit test data with a factory or model constructor, you can consistently test precisely what you want to test.