Fix Edit Department form

[sea-kelp]

Description of Changes

Fix #357:

1. Fix issue where changes were not committed if department did not have associated jobs
2. Fix "Add another rank" button

This wasn't caught by our unit tests because the Flask test client is not triggering database session rollbacks between requests, meaning that uncommitted changes persisted across multiple requests.

Notes for Deployment

None!

Screenshots (if appropriate)

N/A

Tests and linting

• I have rebased my changes on main

• just lint passes

• just test passes

[AetherUnbound]

Tested locally, works as expected! That's unfortunate to hear about the testing 😭