[BUILD-778] chore: Fix flaky tests

[RisingOrange]

Related issues

https://ankihub.atlassian.net/jira/software/c/projects/BUILD/boards/1?selectedIssue=BUILD-778

Proposed changes

• Retry tests which raise coverage.exceptions.DataError using pytest-retry
  • Example test failure: https://github.com/AnkiHubSoftware/ankihub_addon/actions/runs/11445143967/job/31841587157
  • I tried multiple things to do this using pytest-rerunfailures, which is more popular, but it didn't work.
• Fix test_update_feature_flags_in_background test
  • Example for test failure: https://github.com/AnkiHubSoftware/ankihub_addon/actions/runs/11685316727/job/32539850304
  • Use qtbot.wait_until to wait for background thread to perform actions before asserting them