Reduce warnings in tests

[thorbjoernl]

Change Summary

Reduces warnings in tests by explicitly setting flags to enable new iris functionality.

Related issue number

closes #1490
related to #1066

Checklist

• Start with a draft-PR
• The PR title is a good summary of the changes
• PR is set to AeroTools and a tentative milestone
• Documentation reflects the changes where applicable
• Tests for the changes exist where applicable
• Tests pass locally
• Tests pass on CI
• At least 1 reviewer is selected
• Make PR ready to review

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.51%. Comparing base (e478075) to head (29d8214).
Report is 99 commits behind head on main-dev.

Additional details and impacted files

@@            Coverage Diff            @@
##           main-dev    #1502   +/-   ##
=========================================
  Coverage     78.50%   78.51%           
=========================================
  Files           140      140           
  Lines         21285    21291    +6     
=========================================
+ Hits          16710    16716    +6     
  Misses         4575     4575           

Flag	Coverage Δ
unittests	78.51% <100.00%> (+<0.01%)	⬆️

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[lewisblake]

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