Test for duplicate key import

[TingDaoK]

• add a regression test for Fix Memory leak caused by redefinition #626
  • We can see the CI failing for OSX https://github.com/awslabs/aws-c-io/actions/runs/7994446706/job/21832512891 without the fix
  • After the fix, the CI passed
• also re-enable the test for test_concurrent_cert_import, the previous issue seems to be fixed

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 (1779683) 80.04% compared to head (08cc9ce) 80.04%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #627   +/-   ##
=======================================
  Coverage   80.04%   80.04%           
=======================================
  Files          28       28           
  Lines        5949     5949           
=======================================
  Hits         4762     4762           
  Misses       1187     1187           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.