re-enabling and fixing django ci tests

[y3pio]

PR Summary

Re-enabling pipeline steps.

Details

• Since we have our app deployed, re-enabling this CICD step to ensure all future PRs passes these checks.
• Heroku deploy update PR: Ypaing/ponderlab heroku deploy #188
• This PR should fix/address:
  • Re-setup Heroku deployment #186
  • Re-enable django.yml workflow testing step. #178

Testing/QA

• N/A

[y3pio]

@khatchad Looks like the CICD step to run these tests is expecting to create a DB for testing:

Creating test database for alias 'default'...
Got an error creating the test database: (1044, "Access denied for user 'dace[5](https://github.com/ponder-lab/Imperative-DL-Study-Web-App/actions/runs/12959931686/job/36153020001?pr=189#step:5:5)c60l5ctt7og'@'%' to database 'test_uoq6lb032iusvpqz'")

Not sure if our current free setup with JawsDB allows for DB creation. I tried logging into the DB manually to try and create a DB and I'm running into the same permissions error above. -- Will keep digging into an alternate solution for these tests.

[y3pio]

Added test/tests_model.py to test the core model features for some of our models that have business logic. I think this should suffice for now as a possibly temp solution for CI testing without a DB that we can create tables with.

Moved the old tests into OLD_test.py to re-enable at a future date once we have access to a DB with table creation privileges.

Also created #190 to track efforts to create unit tests for views.