Investigate flaky CI test

[thorbjoernl]

Change Summary

There was a small issue with the endtime determination logic, which likely didn't surface locally because of the ordering of the processed files.

Related issue number

#1469

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 78.50%. Comparing base (0eb6381) to head (d07f1a3).
Report is 7 commits behind head on main-dev.

Additional details and impacted files

@@             Coverage Diff              @@
##           main-dev    #1471      +/-   ##
============================================
+ Coverage     78.49%   78.50%   +0.01%     
============================================
  Files           139      139              
  Lines         21090    21101      +11     
============================================
+ Hits          16554    16565      +11     
  Misses         4536     4536              

Flag	Coverage Δ
unittests	78.50% <100.00%> (+0.01%)	⬆️

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