refine RAM role arn credentials provider

[JacksonTian]

You need to complete

• unit tests and/or feature tests
• documentation is changed or added

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 71.29630% with 62 lines in your changes missing coverage. Please review.

Project coverage is 94.60%. Comparing base (cd6b32d) to head (8669e2e).
Report is 1 commits behind head on master.

Files	Patch %	Lines
credentials/internal/providers/http.go	18.51%	44 Missing ⚠️
credentials/internal/utils/utils.go	5.88%	16 Missing ⚠️
credentials/internal/providers/hook.go	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #95      +/-   ##
==========================================
- Coverage   98.16%   94.60%   -3.56%     
==========================================
  Files          23       26       +3     
  Lines        1416     1631     +215     
==========================================
+ Hits         1390     1543     +153     
- Misses         23       85      +62     
  Partials        3        3              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.