Pin databind version to fix pydoc-markdown failure in CI

[ekzhu]

Why are these changes needed?

The latest 4.5.0 release of databind packages causes issue with pydoc-markdown. Force install the 4.4.2 version in CI.

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 36.88%. Comparing base (38b64b6) to head (a50337f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2091   +/-   ##
=======================================
  Coverage   36.88%   36.88%           
=======================================
  Files          68       68           
  Lines        7062     7062           
  Branches     1540     1540           
=======================================
  Hits         2605     2605           
  Misses       4228     4228           
  Partials      229      229           

Flag	Coverage Δ
unittests	36.88% <ø> (ø)

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[sonichi]

Thanks. Depending on how long it takes to find an alternative, we may also need to update other places where pydoc-markdown is used.