BUG: Duplicate _controllers in Flight.TimeNodes.merge()

[zuorenchen]

Pull request type

• Code changes (bugfix, features)
• Code maintenance (refactoring, formatting, tests)
• ReadMe, Docs and GitHub updates
• Other (please describe):

Checklist

• Tests for the changes have been added (if needed)
• Docs have been reviewed and added / updated
• Lint (black rocketpy/ tests/) has passed locally
• All tests (pytest tests -m slow --runslow) have passed locally
• CHANGELOG.md has been updated (if relevant)

Current behavior

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New behavior

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Breaking change

• Yes
• No

Additional information

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.10%. Comparing base (9cf3dd4) to head (38a808a).
⚠️ Report is 30 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #931      +/-   ##
===========================================
+ Coverage    80.27%   81.10%   +0.82%     
===========================================
  Files          104      107       +3     
  Lines        12769    13832    +1063     
===========================================
+ Hits         10250    11218     +968     
- Misses        2519     2614      +95     

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[Gui-FernandesBR]

changelof needs an update before merge