fix: relax dataclasses-json upper bound from <0.5.12 to <0.6.0

[honnix]

Summary

• Relaxes the dataclasses-json upper bound from <0.5.12 to <0.6.0
• The <0.5.12 cap was added when 0.5.12 dropped marshmallow-enum as a transitive dependency (flyte#3873). Since flytekit now declares marshmallow-enum as a direct dependency, 0.5.12–0.5.14 are safe
• The <0.6.0 cap remains because 0.6.0 removes marshmallow-enum support entirely in favor of native Enum, which breaks type_engine.py

Test plan

• Verify flytekit imports succeed with dataclasses-json 0.5.14
• Verify marshmallow_enum.EnumField import in type_engine.py still works

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.58%. Comparing base (d69b3fb) to head (d374667).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3463      +/-   ##
==========================================
+ Coverage   82.94%   83.58%   +0.64%     
==========================================
  Files         264        3     -261     
  Lines       26755      195   -26560     
  Branches     3036        0    -3036     
==========================================
- Hits        22192      163   -22029     
+ Misses       3702       32    -3670     
+ Partials      861        0     -861     

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