Fix AES key size for AES256 in ABI test

[andrewhop]

Issues:

Resolves V1401987253

Description of changes:

This key buffer is too small for the larger key sizes that the test uses.

Call-outs:

It might be worth adding a address sanitizer + ABI test dimension. So far we haven't hit this before so I didn't add a new docker image with everything installed for that.

Testing:

Ran locally and manually reviewed the change for memory safety.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.08%. Comparing base (e587bb5) to head (558d42a).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1629      +/-   ##
==========================================
- Coverage   78.09%   78.08%   -0.01%     
==========================================
  Files         562      562              
  Lines       94656    94666      +10     
  Branches    13574    13573       -1     
==========================================
+ Hits        73923    73924       +1     
- Misses      20140    20146       +6     
- Partials      593      596       +3     

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