fix(api): OperationsManager crash

[dnys1]

Issue #, if available:

• iOS 15 : OperationsManager.removeOperation(cancelToken:) + 84 (OperationsManager.swift:43) #1574

Description of changes:

• Fixes iOS crash due to concurrent access of an array
• Enabled thread sanitizer in API unit tests

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov-commenter]

Codecov Report

Merging #1598 (1b39a40) into main (966d9ed) will increase coverage by 1.52%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1598      +/-   ##
==========================================
+ Coverage   46.17%   47.69%   +1.52%     
==========================================
  Files         260      260              
  Lines       10237    10252      +15     
==========================================
+ Hits         4727     4890     +163     
+ Misses       5510     5362     -148     

Flag	Coverage Δ
android-unit-tests	∅ <ø> (∅)
flutter-unit-tests	36.69% <ø> (ø)
ios-unit-tests	90.79% <100.00%> (+7.21%)	⬆️

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

Impacted Files	Coverage Δ
...xample/ios/unit_tests/FlutterURLSessionTests.swift	87.26% <100.00%> (+87.26%)	⬆️
.../ios/unit_tests/amplify_flutter_exampleTests.swift	35.13% <0.00%> (-59.46%)	⬇️