Fix duplicated label import for Kaggle importer

[wonjuleee]

Summary

How to test

Checklist

• I have added unit tests to cover my changes.​
• I have added integration tests to cover my changes.​
• I have added the description of my changes into CHANGELOG.​
• I have updated the documentation accordingly

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below).

# Copyright (C) 2023 Intel Corporation
#
# SPDX-License-Identifier: MIT

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (5f8ddef) 80.53% compared to head (15f8dee) 80.50%.

❗ Current head 15f8dee differs from pull request most recent head aa0c396. Consider uploading reports for the commit aa0c396 to get more accurate results

Files	Patch %	Lines
src/datumaro/plugins/data_formats/kaggle/base.py	81.81%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1244      +/-   ##
===========================================
- Coverage    80.53%   80.50%   -0.04%     
===========================================
  Files          270      269       -1     
  Lines        30238    30214      -24     
  Branches      5903     5900       -3     
===========================================
- Hits         24353    24323      -30     
- Misses        4506     4509       +3     
- Partials      1379     1382       +3     

Flag	Coverage Δ
ubuntu-20.04_Python-3.8	?
windows-2022_Python-3.8	80.50% <81.81%> (-0.01%)	⬇️

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[vinnamkim]

LGTM.