Disable Account ID Endpoint Mode for Unsigned Requests

[AndrewAsseily]

Issue #, if available: CLI-5255

Description of changes:

• Disabled account ID based endpoint routing when handling unsigned requests.
• Updated test to verify the CLI properly updates the client config to use unsigned requests

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 0.08%. Comparing base (96f96b8) to head (f43ca34).
Report is 54 commits behind head on develop.

Files with missing lines	Patch %	Lines
awscli/customizations/globalargs.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #9334   +/-   ##
=======================================
  Coverage     0.08%   0.08%           
=======================================
  Files          210     210           
  Lines        16984   16983    -1     
=======================================
  Hits            14      14           
+ Misses       16970   16969    -1     

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[ashovlin]

Change looks okay. Please dry-run internally first since we have some integ tests covering --no-sign-request that GitHub Actions won't exercise.