Django-apscheduler

** Fixes **

- Update Github Actions workflow
for [publishing package to PyPi](https://docs.github.com/en/actions/use-cases-and-examples/building-and-testing/building-and-testing-python#publishing-to-pypi).
- Update Github workflow [status badge URL](https://github.com/badges/shields/issues/8671).

**Enhancements**

- Drop support for Python 3.8 and Django 3.2.
- Add support for Python 3.9 to 3.12, Django 4.2 to 5.1
- Bump dependencies to latest available versions.
- Remove pytest-pythonpath as it is no longer needed.
- Add tox.ini file to run tests against all supported versions of Python and Django.
- Update CI configuration to use tox.

**Fixes**

- Take a database lock before updating / deleting job store entries to prevent duplicate key violation errors (thanks
calledbert).

**Fixes**

- Make and commit missing migrations (Resolves [165](https://github.com/jcass77/django-apscheduler/issues/165)).

**Fixes**

- Also handle `db.InterfaceError` when retrying database-related operations (thanks zmmfsj-z).
- Add `unique_job_executions` constraint to ensure that only one `DjangoJobExecution` can be created for
each `DjangoJob` for a specific run time (Mitigates [156](https://github.com/jcass77/django-apscheduler/issues/156)).
- Update CI configuration to test on Django 3.2 and 4.0, and Python 3.10 (
Resolves [163](https://github.com/jcass77/django-apscheduler/issues/163)).
- Drop official support for Django<3.2 and Python<3.8. This is slightly ahead of the official dates published in
https://www.djangoproject.com/download/ and https://devguide.python.org/#status-of-python-branches, but makes the test
workflows simpler and easier to maintain. If you are using older releases they **might** still work...

**Fixes**

- Fix screenshot links in README to work on PyPI.
- Remove reference to deprecated `django.utils.translation.ugettext_lazy`.

**Enhancements**

- The Django admin page will now show a list of all the manually triggered jobs that could not be completed
before `settings.APSCHEDULER_RUN_NOW_TIMEOUT` seconds elapsed.
- Make more of the string output on the admin page Django-translatable.
- Introduce a `retry_on_db_operational_error` utility decorator for retrying database-related operations when
a `django.db.OperationalError` is encountered (Partial resolution
of [145](https://github.com/jcass77/django-apscheduler/issues/145)).
- Introduce a `close_old_connections` utility decorator to enforce Django's `CONN_MAX_AGE` setting. (Partial resolution
of [145](https://github.com/jcass77/django-apscheduler/issues/145) - thanks bluetech). **This decorator should be
applied to all of your jobs that require access to the database.**

**Enhancements**

- Include Python 3.9 in continuous integration runs.
- Switch from Travis-CI to GitHub Actions.