Fixed typo in model.py

[amber-kshz]

Submission Checklist

• Run unit tests
• Declare copyright holder and open-source license: see below

Summary

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• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)

[codecov-commenter]

Codecov Report

Merging #288 into develop will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop     #288   +/-   ##
========================================
  Coverage    76.28%   76.28%           
========================================
  Files            9        9           
  Lines         2197     2197           
========================================
  Hits          1676     1676           
  Misses         521      521           

Impacted Files	Coverage Δ
cmdstanpy/model.py	81.69% <100.00%> (ø)

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[ahartikainen]

Thanks for the PR!