fix: correct none reasoning mapping for small gemini models

[Danidapena]

Before submitting

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• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

Maps None reasoning effort for small gemini models to "none" string

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84%. Comparing base (a370729) to head (ac15643).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@        Coverage Diff         @@
##           main   #65   +/-   ##
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  Coverage    84%   84%           
==================================
  Files         8     8           
  Lines       466   469    +3     
==================================
+ Hits        390   393    +3     
  Misses       76    76           

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[k223kim]

Thank you!