Support negative n in df.head()

[ehsantn]

Changes included in this PR

As title. Fixes a Narwhals test.

Testing strategy

Narwhals test.

User facing changes

Negative n now works.

Checklist

• Pipelines passed before requesting review. To run CI you must include [run CI] in your commit message.
• I am familiar with the Contributing Guide
• I have installed + ran pre-commit hooks.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.71%. Comparing base (c33fbb5) to head (fbb18c7).
⚠️ Report is 159 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #972      +/-   ##
==========================================
+ Coverage   66.68%   67.71%   +1.02%     
==========================================
  Files         186      195       +9     
  Lines       66795    67683     +888     
  Branches     9507     9628     +121     
==========================================
+ Hits        44543    45829    +1286     
+ Misses      19572    19033     -539     
- Partials     2680     2821     +141     

[ehsantn]

CI errors are just flakiness.