chore: remove --max_old_space_size from ci

[sorrycc]

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 #6011 (945299c) into master (de6f76e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #6011   +/-   ##
=======================================
  Coverage   83.05%   83.05%           
=======================================
  Files         157      157           
  Lines        3488     3488           
  Branches      940      934    -6     
=======================================
  Hits         2897     2897           
  Misses        581      581           
  Partials       10       10           

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