Run database dictionary related specs on db/docs changes

What does this MR do and why?

To prevent master broken incidents like gitlab-org/quality/engineering-productivity/master-broken-incidents#6276 (closed) we are mapping changes on db/docs to database dictionary related specs (including spec/db/docs_spec.rb).

List compiled via:

$ rg Database::Dictionary -l spec ee/spec
spec/lib/gitlab/database/sharding_key_spec.rb
spec/lib/gitlab/database/no_new_tables_with_gitlab_main_schema_spec.rb
spec/lib/gitlab/database/dictionary_spec.rb
ee/spec/lib/gitlab/database/desired_sharding_key_spec.rb

See gitlab-org/quality/engineering-productivity/master-broken-incidents#6276 (comment 1906548221)

Contributes to #432986.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

$ tff -f tests.yml db/docs/design_management_repositories.yml
ee/spec/lib/gitlab/database/desired_sharding_key_spec.rb
spec/lib/gitlab/database/dictionary_spec.rb
spec/lib/gitlab/database/no_new_tables_with_gitlab_main_schema_spec.rb
spec/lib/gitlab/database/sharding_key_spec.rb