test(Auth): UserAttributes unit tests

[618coffee]

Issue #, if available:

Description of changes:
Unit tests for

• FetchUserAttributes
• UpdateUserAttributes
• ConfirmUserAttributes

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

[codecov]

Codecov Report

Merging #985 (a4e38b0) into main (0f10e94) will increase coverage by 0.63%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #985      +/-   ##
==========================================
+ Coverage   54.78%   55.41%   +0.63%     
==========================================
  Files         634      634              
  Lines       18372    18372              
==========================================
+ Hits        10065    10181     +116     
+ Misses       8307     8191     -116     

Flag	Coverage Δ
API_plugin_unit_test	48.09% <ø> (+0.12%)	⬆️
AWSPluginsCore	72.41% <ø> (ø)
Amplify	45.79% <ø> (+0.02%)	⬆️
Analytics_plugin_unit_test	73.23% <ø> (ø)
Auth_plugin_unit_test	72.47% <ø> (+5.12%)	⬆️
DataStore_plugin_unit_test	71.02% <ø> (ø)
Predictions_plugin_unit_test	33.48% <ø> (ø)
Storage_plugin_unit_test	57.72% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...n/Operation/AWSGraphQLOperation+APIOperation.swift	50.90% <0.00%> (+3.63%)	⬆️
Amplify/Categories/Hub/HubFilter.swift	57.89% <0.00%> (+5.26%)	⬆️
...AuthPlugin/Dependency/AuthUserServiceAdapter.swift	53.43% <0.00%> (+51.90%)	⬆️
...perations/AWSAuthFetchUserAttributeOperation.swift	88.88% <0.00%> (+55.55%)	⬆️
...erations/AWSAuthUpdateUserAttributeOperation.swift	88.88% <0.00%> (+55.55%)	⬆️
...rations/AWSAuthConfirmUserAttributeOperation.swift	88.88% <0.00%> (+55.55%)	⬆️

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