DOC: Fix documentation for read_csv's mangle_dupe_cols (GH19203)

[Bernhard10]

• [ x] closes Minor inaccurracy in documentation of read_csv's option mangle_dupe_cols #19203

[codecov]

Codecov Report

Merging #19208 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #19208      +/-   ##
==========================================
+ Coverage   91.53%   91.53%   +<.01%     
==========================================
  Files         147      147              
  Lines       48797    48812      +15     
==========================================
+ Hits        44664    44678      +14     
- Misses       4133     4134       +1

Flag	Coverage Δ
#multiple	89.9% <ø> (ø)	⬆️
#single	41.7% <ø> (+0.1%)	⬆️

Impacted Files	Coverage Δ
pandas/io/parsers.py	95.48% <ø> (ø)	⬆️
pandas/core/dtypes/cast.py	87.98% <0%> (-0.68%)	⬇️
pandas/core/internals.py	94.5% <0%> (ø)	⬆️
pandas/core/dtypes/dtypes.py	96.12% <0%> (+0.01%)	⬆️
pandas/core/indexes/interval.py	92.38% <0%> (+0.08%)	⬆️
pandas/core/dtypes/common.py	95.32% <0%> (+0.77%)	⬆️

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[jorisvandenbossche]

Change looks good! Can you check if a similar edit in io.rst is needed?

[jorisvandenbossche]

@Bernhard10 Thanks!