fix(python): Ensure explicit values given to column_widths override autofit in write_excel

[arnabanimesh]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 79.73%. Comparing base (e98e09b) to head (335e7fb).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
py-polars/polars/dataframe/frame.py	50.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20893      +/-   ##
==========================================
- Coverage   79.73%   79.73%   -0.01%     
==========================================
  Files        1566     1566              
  Lines      222681   222681              
  Branches     2572     2572              
==========================================
- Hits       177551   177549       -2     
- Misses      44538    44540       +2     
  Partials      592      592              

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[alexander-beedie]

Makes sense; good catch 👍