Fix docs dotnet core typo

[lach-g]

Why are these changes needed?

Fixed typo in dotnet core documentation.

Related issue number

NA

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.01%. Comparing base (00d6e78) to head (434b30c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6950   +/-   ##
=======================================
  Coverage   81.01%   81.01%           
=======================================
  Files         237      237           
  Lines       18182    18182           
=======================================
  Hits        14730    14730           
  Misses       3452     3452           

Flag	Coverage Δ
unittests	81.01% <ø> (ø)

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