remove upper bound of plugin dependencies for flytekit-polars

[Mecoli1219]

Tracking issue

Why are the changes needed?

1. polars.DataFrame.describe() is not recommended to be used programmatically as suggested by Polars's official documentation, causing the behavior difference in different polars version.
2. frame_equal() is renamed to equals() in version 0.19.16

What changes were proposed in this pull request?

1. Use to_pandas() directly.
2. I changed it into another testing function polars.testing.assert_frame_equal.

How was this patch tested?

Setup process

Screenshots

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Related PRs

Docs link

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.76%. Comparing base (a8f68d7) to head (dc1940d).
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2514      +/-   ##
==========================================
+ Coverage   78.91%   83.76%   +4.84%     
==========================================
  Files         316        3     -313     
  Lines       24965      154   -24811     
  Branches     4012        0    -4012     
==========================================
- Hits        19702      129   -19573     
+ Misses       4548       25    -4523     
+ Partials      715        0     -715     

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[pingsutw]

lgtm, thank you!