Print slow tests in CI

[jackgerrits]

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-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 44.88%. Comparing base (7739632) to head (0a91220).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2082      +/-   ##
==========================================
+ Coverage   36.90%   44.88%   +7.97%     
==========================================
  Files          68       68              
  Lines        7061     7061              
  Branches     1541     1669     +128     
==========================================
+ Hits         2606     3169     +563     
+ Misses       4225     3603     -622     
- Partials      230      289      +59     

Flag	Coverage Δ
unittests	44.86% <ø> (+7.95%)	⬆️

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