Copy sibling fields to avoid changing parent unit (bugfix)

[Hook25]

Description

Not copying is alway wrong here. It worked before because all mutations that we were doing were over string, which are immutable, so they automatically would copy. This leads to a funny bugs like flags of the parent unit being modified when sibiling unit is modified.

Resolved issues

Discovered while working on: https://warthogs.atlassian.net/browse/CHECKBOX-2200

Documentation

N/A

Tests

N/A (Change is really small, I don't even know how to test it)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.92%. Comparing base (475d7e7) to head (4516742).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2497      +/-   ##
==========================================
- Coverage   58.92%   58.92%   -0.01%     
==========================================
  Files         476      476              
  Lines       48027    48025       -2     
  Branches     8571     8571              
==========================================
- Hits        28302    28300       -2     
  Misses      18833    18833              
  Partials      892      892              

Flag	Coverage Δ
checkbox-ng	76.06% <100.00%> (-0.01%)	⬇️

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