[CI] Cancel previous runs that are not completed

[wangruohui]

Follow open-mmlab/mmcv#1537

[wangruohui]

As a test, this action is canceled after a new commit.

[codecov]

Codecov Report

Merging #650 (621e6ff) into master (317723e) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #650      +/-   ##
==========================================
+ Coverage   80.47%   80.51%   +0.03%     
==========================================
  Files         198      198              
  Lines       11233    11233              
  Branches     1795     1795              
==========================================
+ Hits         9040     9044       +4     
+ Misses       1916     1914       -2     
+ Partials      277      275       -2     

Flag	Coverage Δ
unittests	80.48% <ø> (+0.02%)	⬆️

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Impacted Files	Coverage Δ
...ls/components/stylegan2/generator_discriminator.py	86.14% <0.00%> (+2.40%)	⬆️

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