optimize func ConvertToRegistryAuths

[zmberg]

Ⅰ. Describe what this PR does

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how to verify it

Ⅳ. Special notes for reviews

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 48.59%. Comparing base (9913b92) to head (141bb45).
Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1492      +/-   ##
==========================================
- Coverage   48.60%   48.59%   -0.01%     
==========================================
  Files         157      157              
  Lines       22480    22480              
==========================================
- Hits        10926    10924       -2     
- Misses      10352    10353       +1     
- Partials     1202     1203       +1     

Flag	Coverage Δ
unittests	48.59% <ø> (-0.01%)	⬇️

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[kruise-bot]

@zmberg: PR needs rebase.

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