fix: Fix cum_max using exception text of cum_min for invalid dtype

[t-ded]

closes #18754

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.82%. Comparing base (6561eba) to head (b95d287).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-ops/src/series/ops/cum_agg.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18780      +/-   ##
==========================================
- Coverage   79.84%   79.82%   -0.02%     
==========================================
  Files        1518     1518              
  Lines      205576   205576              
  Branches     2892     2892              
==========================================
- Hits       164132   164111      -21     
- Misses      40896    40917      +21     
  Partials      548      548              

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[ritchie46]

Thanks!