Fix error when tests run in parallel.

[graebm]

Issue:
Rare chance of failure when tests run in parallel.

The issue was that many tests need to write, then read, an SSO token file at $HOME/.aws/sso/cache/<xyz>.json. But if multiple tests run in parallel, they could each write different stuff to that file, and then read the contents that some OTHER test put there.

Description of changes:
Each test creates a random tmp directory and uses that as $HOME

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

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (baeffa7) 79.44% compared to head (9107251) 79.51%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #221      +/-   ##
==========================================
+ Coverage   79.44%   79.51%   +0.06%     
==========================================
  Files          33       33              
  Lines        5798     5798              
==========================================
+ Hits         4606     4610       +4     
+ Misses       1192     1188       -4     

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