Investigate increased wait time for some DAST specs

DAST specs in ee/spec/features/projects/security/user_creates_on_demand_scan_spec.rb recently started failing due to the error:

Timeout (30s) reached while running a waiting Capybara finder.
            Consider using a non-waiting finder.

An MR was created to increase the wait time to 1 minute: !150838 (merged)

Investigate why the tests became flaky suddenly and if the wait time can be reduced.