Fix refresh of Bedrock models and remove some expired credentials from cassettes

[tpaulshippy]

Purpose

In the process of building #50 I made a couple of mistakes.

1. I ran the model refresh tests while credentials were not set to mask, bleeding them into the cassettes.
2. I modified the signing code in such a way to break the model refresh.

Approach

Fix the second issue and then rerun the model refresh tests to fix the first.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.11%. Comparing base (3fe4b12) to head (87953ff).
Report is 10 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #89   +/-   ##
=======================================
  Coverage   92.11%   92.11%           
=======================================
  Files          71       71           
  Lines        2586     2588    +2     
  Branches      377      378    +1     
=======================================
+ Hits         2382     2384    +2     
  Misses        204      204           

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