pytest.ini: Fix 'pytest-postgresql < 4' support with 'pytest >= 8'

pytest 8.0 modified the handling of default parameter when defining
configuration options, which breaks the use of 'pytest-postgresql < 4'.

Workaround that issue by explicitly defining postgresql_load option
in pytest.ini file.

See https://github.com/pytest-dev/pytest/issues/11282.

pytest.ini

@@ -16,3 +16,5 @@ filterwarnings =
     ignore:.*'U' mode is deprecated
 
 asyncio_mode = strict
+# fix 'pytest-postgresql < 4' support with 'pytest >= 8'
+postgresql_load =