Fix typo

[weijen]

Just fix typo

Why are these changes needed?

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation 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 77.87%. Comparing base (5c969d3) to head (6c29d13).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5361      +/-   ##
==========================================
+ Coverage   77.85%   77.87%   +0.02%     
==========================================
  Files         158      158              
  Lines        9520     9520              
==========================================
+ Hits         7412     7414       +2     
+ Misses       2108     2106       -2     

Flag	Coverage Δ
unittests	77.87% <ø> (+0.02%)	⬆️

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