Limit opencv-python version

[ckkelvinchan]

Motivation

The latest opencv-python causes error in CI. This PR limits the version of it.

Modification

Modify requirements/runtime.txt

[codecov]

Codecov Report

Merging #689 (bbe66c0) into master (4f814a8) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #689      +/-   ##
==========================================
+ Coverage   80.59%   80.61%   +0.01%     
==========================================
  Files         200      200              
  Lines       11419    11419              
  Branches     1831     1831              
==========================================
+ Hits         9203     9205       +2     
+ Misses       1932     1931       -1     
+ Partials      284      283       -1     

Flag	Coverage Δ
unittests	80.58% <ø> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
...ls/components/stylegan2/generator_discriminator.py	86.14% <0.00%> (+1.20%)	⬆️

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[Yshuo-Li]

Lint failed

[ckkelvinchan]

Lint failed

It passed now, but some CIs still failed. Could you help have a look?