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

• 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

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