Fix DII unittests for newer Python versions

[FelixWodaczek]

Proposed changes

numpy and pytest deprecations have made some unittests crash in newer python versions. Small changes in unittests to account for this

Types of changes

• [x] Bugfix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• [x] Lint and unit tests pass locally with my changes
• [x] I have added tests that prove my fix is effective or that my feature works