[Core] Fix openai dependency error introduced when merging #1044

[ekzhu]

Why are these changes needed?

Fix dependency error introduced when merging #1044. The openai package version constraint should be >1.3. Removing the constraint <1.5 which was introduced by error.

Related issue number

#1044

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 ✅

Comparison is base (d583ad8) 30.14% compared to head (b3a1ee2) 58.55%.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1071       +/-   ##
===========================================
+ Coverage   30.14%   58.55%   +28.40%     
===========================================
  Files          30       30               
  Lines        4020     4020               
  Branches      908      957       +49     
===========================================
+ Hits         1212     2354     +1142     
+ Misses       2729     1441     -1288     
- Partials       79      225      +146     

Flag	Coverage Δ
unittests	58.35% <ø> (+28.25%)	⬆️

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