Add helpful tip on debugging a failing CI spec

* Came up here: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/103434#note_1172316521

doc/development/testing_guide/flaky_tests.md

@@ -31,6 +31,9 @@ it's reset to a pristine test after each test.
   inconsistent state, so that following tests might not know about certain columns.
 - [Example 2](https://gitlab.com/gitlab-org/gitlab/-/issues/368500): A test modifies data that is
   used by a following test.
+- [Example 3](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/103434#note_1172316521): A test for a database query passes in a fresh database, but in a 
+  CI/CD pipeline where the database is used to process previous test sequences, the test fails. This likely
+    means that the query itself needs to be updated to work in a non-clean database.
 
 ### Ordering assertion
 

doc/development/testing_guide/index.md

@@ -53,7 +53,7 @@ tips and tricks to get the most out of white-box testing.
 What are flaky tests, the different kind of flaky tests we encountered, and what
 we do about them.
 
-## [GitLab pipelines](../pipelines.md)
+## [GitLab pipelines](../pipelines/index.md)
 
 How GitLab test suite is run in the CI context: setup, caches, artifacts,
 parallelization, monitoring.