mypy in pre-commit fixed

[davorrunje]

Why are these changes needed?

It fixes the problem of importing optional targets to check typing with mypy in pre-commit.

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 36.90%. Comparing base (a6a7409) to head (997d9d5).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2117   +/-   ##
=======================================
  Coverage   36.90%   36.90%           
=======================================
  Files          68       68           
  Lines        7061     7061           
  Branches     1541     1541           
=======================================
  Hits         2606     2606           
  Misses       4225     4225           
  Partials      230      230           

Flag	Coverage Δ
unittests	36.90% <ø> (ø)

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