feat(admin): add task field to search_fields

[kyonlee]

Extended the search functionality in the PeriodicTaskAdmin by adding 'task' to the search_fields. This allows users to search periodic tasks by their task names, improving the admin interface usability.

Issue: #856

[auvipy]

can you please check why the builds are failing?

[kyonlee]

It looks like the builds were failing due to a flaky test (t/unit/test_schedulers.py::test_DatabaseScheduler::test_get_excluded_hours_for_crontab_tasks), introduced in fc64741.

The test does not account for the default Celery cleanup task hour, causing it to fail when ran at specific times.
https://github.com/celery/django-celery-beat/blob/main/django_celery_beat/schedulers.py#L414

I do not think fixing this test is within scope of this PR, but I'm happy to open a separate PR to address it. Let me know how you would like me to approach it. e.g. freezing time, assert only if statements do not result in '4', etc.

[auvipy]

it would be highly appreciated if you can open a separate PR to address this flaky test. I will ping @alirafiei75 to review it

[kyonlee]

Here's the PR that will remove the flake from `t/unit/test_schedulers.py::test_DatabaseScheduler::test_get_excluded_hours_for_crontab_tasks 🙏

[alirafiei75]

I have reviewed the mentioned PR and approved it. @kyonlee thanks for fixing the test.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.42%. Comparing base (a70a9dc) to head (d25d22c).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #857   +/-   ##
=======================================
  Coverage   87.42%   87.42%           
=======================================
  Files          32       32           
  Lines         954      954           
  Branches       76       76           
=======================================
  Hits          834      834           
  Misses        102      102           
  Partials       18       18           

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