Document rspec_check_order_dependence in flaky specs docs

I discovered by asking around that there is another tool documented at
https://docs.gitlab.com/ee/development/testing_guide/best_practices.html#test-order
for dealing with ordering issues. The `rspec_bisect_flaky` is actually
broken for most people at the moment due to some OSX issue which is
being discussed in this
[Slack thread (internal)](https://gitlab.slack.com/archives/C2Z9A056E/p1727723530427539)
.

In order to help people with debugging these flaky specs I thought I
should also document this other useful tool.

doc/development/testing_guide/unhealthy_tests.md

@@ -338,7 +338,14 @@ These flaky tests can fail depending on the order they run with other tests. For
 - <https://gitlab.com/gitlab-org/gitlab/-/issues/327668>
-To identify the tests that lead to such failure, we can use `scripts/rspec_bisect_flaky`,
+To identify test ordering issues in a single file you can run
+`scripts/rspec_check_order_dependence`:
+
+```shell
+scripts/rspec_check_order_dependence spec/models/project_spec.rb
+```
+
+To identify the ordering issues across different files, you can use `scripts/rspec_bisect_flaky`,
 which would give us the minimal test combination to reproduce the failure:
 1. First obtain the list of specs that ran before the flaky test. You can search