chore: fix flaky weight test

[zhaohuabing]

fix: #7572

This PR uses the same weight and offset as the other weighted routing tests, so hopefully it won't be flaky anymore.

eighted_backend.go:172: The actual success count is not within the expected range, success 46

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.35%. Comparing base (0d0c230) to head (935fb28).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7574      +/-   ##
==========================================
+ Coverage   72.32%   72.35%   +0.02%     
==========================================
  Files         232      232              
  Lines       34109    34109              
==========================================
+ Hits        24669    24679      +10     
+ Misses       7670     7661       -9     
+ Partials     1770     1769       -1     

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