Remove setUpTestData from PlaywrightTestCase

[jedie]

Remove setUpTestData from PlaywrightTestCase because it doesn't work call this from
setUpClass, because all data will be removed after the first test.

The PlaywrightTestCase used StaticLiveServerTestCase that inherits from TransactionTestCase
that will flush the database after each tests.

The LiveServerTestCase doc string says:

It inherits from TransactionTestCase instead of TestCase because the
threads don't share the same transactions (unless if using in-memory sqlite)
and each thread needs to commit all their transactions so that the other
thread can see the changes.

See also: https://code.djangoproject.com/ticket/23640

We can call setUpTestData from setUp. But the class method setUpTestData originally stands for
initializing test data for the entire test case, so don't do this. It's up to the child class how to
create initial test data.

Raise a warning if there is a setUpTestData to clarify that it's not usable.

Additional fixes:

Remove pytest warning by add the marker to [tool.pytest.ini_options]:

PytestUnknownMarkWarning: Unknown pytest.mark.playwright - is this a typo?  You can register custom
marks to avoid this warning - for details, see https://docs.pytest.org/en/stable/how-to/mark.html
    @pytest.mark.playwright

Split github actions PyPi cache, see: python-poetry/poetry#4568

[codecov-commenter]

Codecov Report

Merging #67 (ed4ebc6) into master (6edc656) will decrease coverage by 0.03%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master      #67      +/-   ##
==========================================
- Coverage   94.90%   94.87%   -0.04%     
==========================================
  Files         100      100              
  Lines        3611     3608       -3     
==========================================
- Hits         3427     3423       -4     
- Misses        184      185       +1     

Impacted Files	Coverage Δ
bx_django_utils/test_utils/playwright.py	58.53% <0.00%> (-2.18%)	⬇️
bx_django_utils/__init__.py	100.00% <100.00%> (ø)
...django_utils_tests/tests/test_playwright_helper.py	67.85% <100.00%> (-1.11%)	⬇️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.