[Fix] fix a bug in multi-label classification

[Dai-Wenxun]

Motivation

#2416
fix a bug in multi-label classification.

Modification

Check whether is single-label before adding to the self.results.

if label['item'].size(0) == 1:
    # single-label
    result['label'] = label['item'].item()
else:
    # multi-label
    result['label'] = label['item'].cpu().numpy()

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01 ⚠️

Comparison is base (07259a2) 76.97% compared to head (87440b9) 76.96%.

❗ Current head 87440b9 differs from pull request most recent head ac4c183. Consider uploading reports for the commit ac4c183 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2425      +/-   ##
==========================================
- Coverage   76.97%   76.96%   -0.01%     
==========================================
  Files         159      159              
  Lines       12546    12541       -5     
  Branches     2099     2098       -1     
==========================================
- Hits         9657     9652       -5     
  Misses       2386     2386              
  Partials      503      503              

Flag	Coverage Δ
unittests	76.96% <100.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
mmaction/models/heads/base.py	80.95% <ø> (ø)
mmaction/__init__.py	100.00% <100.00%> (ø)
mmaction/evaluation/metrics/acc_metric.py	81.29% <100.00%> (-0.70%)	⬇️
mmaction/models/losses/cross_entropy_loss.py	65.27% <100.00%> (+0.48%)	⬆️

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