Adjust role used by GitHub action that builds docs.

[ashovlin]

Issue #, if available: N/A

Description of changes:

1. Fixes a CI failure on fix: Enable selecting the '.NET 6 on AL2023' platform when deploying to Elastic Beanstalk on Linux #807. We recently adjusted some internal accounts where we run integration tests, so CI_AWS_ROLE_ARN is no longer valid. This reuses the CI_MAIN_TESTING_ACCOUNT_ROLE_ARN instead.
   • The doc generator uses server mode, which requires AWS credentials to pass its health check. I didn't actually see it make any requests when running locally.
2. Also upgraded the credential action while here, there was a warning about old Node versions.

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[ashovlin]

I think we tore this down while performing maintenance on the account it maps to. Let me know if you don't think its appropriate to reuse CI_MAIN_TESTING_ACCOUNT_ROLE_ARN for this use case.

[philasmar]

i think ideally we should use this account to determine which test runner to use, but i'm fine with this for now.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8990861) 32.34% compared to head (73076dd) 61.44%.
Report is 1 commits behind head on dev.

Additional details and impacted files

@@             Coverage Diff             @@
##              dev     #808       +/-   ##
===========================================
+ Coverage   32.34%   61.44%   +29.09%     
===========================================
  Files         271      277        +6     
  Lines       10604    10659       +55     
  Branches     1474     1484       +10     
===========================================
+ Hits         3430     6549     +3119     
+ Misses       6885     3568     -3317     
- Partials      289      542      +253     

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