docs(python): Improve Expr.name.map docstring example

[alexander-beedie]

Closes #21305.

(removesuffix was made available in py3.9, which has been our minimum supported version for a while now; updated the example to use it, as per the linked issue).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.92%. Comparing base (5e51218) to head (efbb668).
Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21309      +/-   ##
==========================================
+ Coverage   79.82%   79.92%   +0.09%     
==========================================
  Files        1596     1596              
  Lines      228565   228642      +77     
  Branches     2608     2615       +7     
==========================================
+ Hits       182462   182737     +275     
+ Misses      45507    45307     -200     
- Partials      596      598       +2     

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