fix flaky random bip32 test

[fuxingloh]

What kind of PR is this?:

/kind fix

What this PR does / why we need it:

fixed flaky random bip32 test

[github-actions]

size-limit report 📦

Path	Size	Loading time (3g)	Running time (snapdragon)	Total time
packages/jellyfish/dist/jellyfish.umd.js	18.19 KB (0%)	364 ms (0%)	160 ms (+0.23% 🔺)	523 ms

[codecov]

Codecov Report

Merging #156 (c2548a4) into main (5d8e2e4) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #156      +/-   ##
==========================================
+ Coverage   95.34%   95.39%   +0.04%     
==========================================
  Files          50       51       +1     
  Lines        1074     1085      +11     
  Branches      130      131       +1     
==========================================
+ Hits         1024     1035      +11     
  Misses         48       48              
  Partials        2        2              

Impacted Files	Coverage Δ
...jellyfish-transaction/src/buffer/buffer_varuint.ts	100.00% <ø> (ø)
...llyfish-transaction/src/buffer/buffer_bignumber.ts	100.00% <100.00%> (ø)
...ellyfish-transaction/src/buffer/buffer_composer.ts	98.57% <100.00%> (-0.06%)	⬇️
packages/jellyfish-transaction/src/tx_signature.ts	95.83% <100.00%> (+0.05%)	⬆️

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