Analysis View backend: test for future DB changes

[MetRonnie]

Problem

Tests added in #434 manually create the task_jobs table. However if the DB structure changes in cylc-flow then the tests will not reflect the true DB. However we do need to ensure backwards compatibility so manually creating the table using the current format is valid.

Proposed Solution

We need to do both:

• [x] Test using manually created table
• [ ] Test using automatically created table using

  with CylcWorkflowDAO(':memory:', create_tables=True) as dao:
      ...