Remind developers to adjust exclusions for seeded tables in specs

What does this MR do and why?

When tables are seeded in specs. These tables should be excluded from record deletions to prevent flaky specs.

This commit adds a code comment as a breadcrumb.

See gitlab-org/quality/engineering-productivity/master-broken-incidents#3905 (closed)

This implements the "Naive approach" from gitlab-org/quality/engineering-productivity/master-broken-incidents#3905 (comment 1608837085).

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