Decrease example size for polynomial doe

[berland]

Having the size at 1000 just takes a lot of minutes during
testing and does not increase test coverage. Reduced to an
ensemble size of 50.

Pre review checklist

• Added appropriate release note label
• PR title captures the intent of the changes, and is fitting for release notes.
• Commit history is consistent and clean, in line with the contribution guidelines.

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[codecov-commenter]

Codecov Report

Merging #3304 (6dd9f14) into main (bdb2615) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #3304      +/-   ##
==========================================
+ Coverage   64.87%   64.89%   +0.02%     
==========================================
  Files         615      615              
  Lines       48355    48355              
  Branches     4359     4359              
==========================================
+ Hits        31369    31379      +10     
+ Misses      15531    15528       -3     
+ Partials     1455     1448       -7     

Impacted Files	Coverage Δ
ert/data/record/_transformation.py	89.04% <0.00%> (+0.47%)	⬆️
libres/lib/enkf/block_fs_driver.cpp	72.51% <0.00%> (+0.58%)	⬆️
ert_gui/simulation/run_dialog.py	80.30% <0.00%> (+0.75%)	⬆️
libres/lib/res_util/block_fs.cpp	53.00% <0.00%> (+1.38%)	⬆️

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