Query timeout issues on `Security::Scans::PurgeWorker`

https://sentry.gitlab.net/gitlab/gitlabcom/issues/4017896/?referrer=gitlab_plugin

PG::QueryCanceled: ERROR:  canceling statement due to statement timeout

  lib/gitlab/database/load_balancing/connection_proxy.rb:100:in `block in read_using_load_balancer'
    connection.send(...)
  lib/gitlab/database/load_balancing/load_balancer.rb:129:in `block in read_write'
    yield connection
  lib/gitlab/database/load_balancing/load_balancer.rb:207:in `retry_with_backoff'
    return yield attempt # Yield the current attempt count
  lib/gitlab/database/load_balancing/load_balancer.rb:118:in `read_write'
    retry_with_backoff(attempts: attempts) do |attempt|
  lib/gitlab/database/load_balancing/connection_proxy.rb:99:in `read_using_load_balancer'
    @load_balancer.read_write do |connection|
...
(142 additional frame(s) were not displayed)

ActiveRecord::QueryCanceled: PG::QueryCanceled: ERROR:  canceling statement due to statement timeout

PG::QueryCanceled: ERROR:  canceling statement due to statement timeout