Fix: Corrected typo in o4-mini model name and fixed endpoint map

[bakatz]

Describe the change
Someone typo'd the O4 mini model name in #968. Fixed it in this PR.

Provide OpenAI documentation link
N/A

Describe your solution
Self-explanatory

Tests
Tests didn't need to be updated as this was a variable naming change only. The underlying model name was correct.

Additional context
See this issue

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.44%. Comparing base (774fc9d) to head (23db2c6).
Report is 98 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #981       +/-   ##
===========================================
- Coverage   98.46%   85.44%   -13.02%     
===========================================
  Files          24       43       +19     
  Lines        1364     2268      +904     
===========================================
+ Hits         1343     1938      +595     
- Misses         15      308      +293     
- Partials        6       22       +16     

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[bakatz]

@sashabaranov please take a look, this should be a quick one (really)

[sashabaranov]

Thank you!