Add debug info and try to fix intermittent seed tests

[zetter-rpf]

This attempts to fix an intermittent test failures in https://app.circleci.com/pipelines/github/RaspberryPiFoundation/editor-api/2939/workflows/789aa8a3-0910-4101-817d-a908c8fbcfa3/jobs/5584

Related unmerged attempt to fix: #600
Related previous attempt to fix: #579

I can't see anything in the code I think would cause the missing or additional records which makes me think it's likely to be a transactional/test cleanup issue.

What's changed?

• Added logging to tell use the state of the database if test fails again
• Changed database cleaner strategy to see if transactions are causing the issue

See commits for more details

Logs

The failing tests:

  1) for_education :seed_a_school_with_lessons_and_students adds two projects
     Failure/Error: expect(Project.where(lesson_id: lesson.pluck(:id)).length).to eq(2)
     
       expected: 2
            got: 4
     
       (compared using ==)
     # ./spec/lib/tasks/for_education_spec.rb:80:in `block (3 levels) in <top (required)>'
     # ./spec/rails_helper.rb:108:in `block (3 levels) in <top (required)>'
     # ./spec/rails_helper.rb:106:in `block (2 levels) in <top (required)>'

  2) test_seeds :seed_a_school_with_lessons_and_students creates a class teacher association for the teacher
     Failure/Error: expect(ClassTeacher.where(teacher_id:).length).to eq(1)
     
       expected: 1
            got: 0
     
       (compared using ==)
     # ./spec/lib/test_seeds_spec.rb:82:in `block (3 levels) in <top (required)>'
     # ./spec/rails_helper.rb:108:in `block (3 levels) in <top (required)>'
     # ./spec/rails_helper.rb:106:in `block (2 levels) in <top (required)>'