Update db:migrate-from-previous-major-version

What does this MR do?

Related to #337620 (closed)

In db:migrate-from-previous-major-version we verify that database migrations between major GitLab versions apply cleanly.

We've been on 14.x for a while now, so we were now testing the 12.x -> 14.x path i.e. two major version upgrades.

This MR updates this job to test 13.x -> 14.x instead.

This should also help us fix a problem with a Ruby 3 incompatibility related to an old version of asana that was on the 12.x path.

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.