Revert the Python 3.11 exclusion for date isoformat (#32490)

The official Python image for 3.11 had a brief period when the
date `20120503` has been an acceptable date, but it is not
accepted as of 3.11.4 release on 5th of July.

This PR reverts  the changes in tests implemented in #27264 to
accomodate for it and brings back the date as error case.

tests/models/test_param.py

@@ -20,7 +20,6 @@
 
 import pytest
 
-from airflow import PY311
 from airflow.decorators import task
 from airflow.exceptions import ParamValidationError, RemovedInAirflow3Warning
 from airflow.models.param import Param, ParamsDict
@@ -127,25 +126,20 @@ def test_string_time_format(self):
  "date_string",
  [
  "2021-01-01",
- pytest.param(
- "20120503",
- marks=pytest.mark.skipif(not PY311, reason="Improved fromisoformat() in 3.11."),
- ),
  ],
  )
  def test_string_date_format(self, date_string):
  """Test string date format."""
  assert Param(date_string, type="string", format="date").resolve() == date_string
 
+ # Note that 20120503 behaved differently in 3.11.3 Official python image. It was validated as a date
+ # there but it started to fail again in 3.11.4 released on 2023-07-05.
  @pytest.mark.parametrize(
  "date_string",
  [
  "01/01/2021",
  "21 May 1975",
- pytest.param(
- "20120503",
- marks=pytest.mark.skipif(PY311, reason="Improved fromisoformat() in 3.11."),
- ),
+ "20120503",
  ],
  )
  def test_string_date_format_error(self, date_string):