fix lint

[triple-Mu]

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Motivation

Please describe the motivation of this PR and the goal you want to achieve through this PR.

Modification

Please briefly describe what modification is made in this PR.

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repos?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMCls.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[codecov]

Codecov Report

Base: 64.42% // Head: 64.42% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (f537043) compared to base (b955832).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #9685      +/-   ##
==========================================
- Coverage   64.42%   64.42%   -0.01%     
==========================================
  Files         370      370              
  Lines       30036    30036              
  Branches     5008     5008              
==========================================
- Hits        19352    19350       -2     
- Misses       9651     9652       +1     
- Partials     1033     1034       +1     

Flag	Coverage Δ
unittests	64.41% <ø> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmdet/core/bbox/samplers/random_sampler.py	75.00% <0.00%> (-5.56%)	⬇️

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