chore: upgrade mini-css-extract-plugin

[ycjcl868]

The PR just upgrade mini-css-extract-plugin version

sourceMap TODO:
ref: #5817
ref: faceyspacey/extract-css-chunks-webpack-plugin#293
ref: webpack-contrib/mini-css-extract-plugin#529
ref: webpack-contrib/mini-css-extract-plugin#29

Checklist

• npm test passes
• tests are included
• documentation is changed or added
• commit message follows commit guidelines

Description of change

• any feature?
• close https://github.com/umijs/umi/ISSUE_URL

[codecov]

Codecov Report

Merging #5818 (4f40820) into master (8276fa1) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5818   +/-   ##
=======================================
  Coverage   83.37%   83.37%           
=======================================
  Files         155      155           
  Lines        3465     3465           
  Branches      934      914   -20     
=======================================
  Hits         2889     2889           
- Misses        567      568    +1     
+ Partials        9        8    -1     

Impacted Files	Coverage Δ
packages/bundler-webpack/src/getConfig/css.ts	92.85% <ø> (ø)
packages/core/src/Config/Config.ts	61.78% <0.00%> (ø)

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