Fix unstructured deps installation error

[thinkall]

Why are these changes needed?

Fix errors of Test RetrieveChat

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-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 49.80%. Comparing base (a27bda8) to head (c692701).

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2248       +/-   ##
===========================================
+ Coverage   36.52%   49.80%   +13.27%     
===========================================
  Files          77       77               
  Lines        7780     7780               
  Branches     1666     1803      +137     
===========================================
+ Hits         2842     3875     +1033     
+ Misses       4699     3583     -1116     
- Partials      239      322       +83     

Flag	Coverage Δ
unittest	14.37% <ø> (?)
unittests	48.74% <ø> (+12.22%)	⬆️

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