Use larger instance for c6g fips

[samuel40791765]

Description of changes:

c6g on the ec2-test-framework has been slowing down considerably with our recent FIPS changes.

Call-outs:

N/A

Testing:

N/A

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 78.47%. Comparing base (ad93747) to head (f4f7f46).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1899      +/-   ##
==========================================
+ Coverage   78.45%   78.47%   +0.01%     
==========================================
  Files         585      585              
  Lines       99516    99516              
  Branches    14244    14242       -2     
==========================================
+ Hits        78080    78096      +16     
+ Misses      20796    20786      -10     
+ Partials      640      634       -6     

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