fix: Fix quoting style of decimal csv output

[ritchie46]

fixes #19293

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 80.01%. Comparing base (dae6cd9) to head (940130f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...s/polars-io/src/csv/write/write_impl/serializer.rs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #19298   +/-   ##
=======================================
  Coverage   80.00%   80.01%           
=======================================
  Files        1528     1528           
  Lines      209850   209843    -7     
  Branches     2419     2419           
=======================================
+ Hits       167894   167909   +15     
+ Misses      41405    41383   -22     
  Partials      551      551           

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