fix: Pin amazon-braket-sdk version to 1.81.0

[rmshaffer]

Issue #, if available:
#34

Description of changes:
This is a temporary workaround for #34 which will allow CI to pass again while a full fix is developed.

Testing done:
tox and CI

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (e2bb431) to head (16a20b2).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #35   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           49        49           
  Lines         2090      2090           
  Branches       345       345           
=========================================
  Hits          2090      2090           

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