Fix state leak from language ID constraint migration specs

What does this MR do and why?

Removes the add_constraint call from the after hook in spec/migrations/20260811122029_add_programming_languages_language_id_not_null_constraint_spec.rb and spec/migrations/20260811122031_add_repository_languages_language_id_not_null_constraint_spec.rb. The hooks now only drop the constraint.

Since 2026-09-22, spec/migrations/20260807142854_remove_programming_languages_without_language_id_spec.rb fails on master with PG::CheckViolation: new row for relation "programming_languages" violates check constraint "check_4e6f0ff707".

check_4e6f0ff707 is only added when Gitlab.com_except_jh? is true and is not in db/structure.sql, so it does not exist in the test database unless a spec adds it. The after hook re-added it after each example. When that spec runs before the removal spec in the same process, the constraint is still present. The removal spec's schema_migrate_down! runs before its before block stubs Gitlab.com_except_jh?, so the constraint migration's down is a no-op and the constraint stays. Inserting a row with language_id: nil then fails.

RSpec test balancing runs files longest expected duration first. In job logs from 2026-09-22 the constraint spec's expected duration went from 63 s to 70 s while the removal spec's went from 68 s to 60 s, so the constraint spec now runs first when both land on the same node.

The repository_languages spec has the same hook and gets the same change. No current spec is affected by it.

References

• Master job showing the failure: https://gitlab.com/gitlab-org/gitlab/-/jobs/16664711359
• CI health incident for this spec file: https://gitlab.com/gitlab-org/quality/analytics/ci-health-incidents/-/work_items/1308
• CI health incident for the rails_pg_check_violation category: https://gitlab.com/gitlab-org/quality/analytics/ci-health-incidents/-/work_items/1309
• MR that added the after hooks: !247554 (merged)

Screenshots or screen recordings

Not applicable, spec-only change.

How to set up and validate locally

On master, run:

bin/rspec spec/migrations/20260811122029_add_programming_languages_language_id_not_null_constraint_spec.rb spec/migrations/20260807142854_remove_programming_languages_without_language_id_spec.rb

Three examples fail. On this branch the same command passes. Reversing the file order on master also passes.

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