[backport -> release/3.7.x] tests(ci): fix migration test failed to run when updating migration files for an unreleased version

[team-gateway-bot]

Automated backport to release/3.7.x, triggered by a label in #13134.

Original description

Summary

This PR fixes an issue that migration tests will fail when the migration files for the next unreleased version get updated.

It has created a PR base branch next/3.4.x.x. Add migration scripts to the existing script file, such as kong/enterprise_edition/db/migrations/enterprise/021_3435_to_3436.lua. It will be ignored when executing kong migrations up.

case 1: upgrade next/2.8.x.x to the current PR of the next/3.4.x.x. the migration 021_3435_to_3436.lua is always new.
The upgrade_tests are work well.

case 2: Upgrade next/3.4.x.x to the current PR of next/3.4.x.x. When starting the next/3.4.x.x container, the migration script 021_3435_to_3436.lua will be bootstrapped for the first time. Then, upgrade to this PR. The second time using kong migrations up to bootstrap the script will not execute the migration script 021_3435_to_3436.lua.

There is an example. https://github.com/Kong/kong-ee/actions/runs/9310936847/job/25629308613

Checklist

• The Pull Request has tests
• A changelog file has been added to CHANGELOG/unreleased/kong or adding skip-changelog label on PR if unnecessary. README.md
• The Pull Request has backports to all the versions it needs to cover
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE