ci: update rotate-keys for additional key

[scotthart]

No description provided.

[gemini-code-assist]

Code Review

This pull request refactors the key rotation script rotate-keys.sh to support multiple service accounts, specifically adding the observability service account. The feedback recommends assigning command substitution outputs to variables to prevent swallowing errors under set -e, and refactoring the space-separated file types into a Bash array to avoid unquoted variable expansion issues.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.27%. Comparing base (fd956fb) to head (db50235).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16269      +/-   ##
==========================================
- Coverage   92.27%   92.27%   -0.01%     
==========================================
  Files        2218     2218              
  Lines      206654   206654              
==========================================
- Hits       190699   190687      -12     
- Misses      15955    15967      +12     

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