[Flaky test] `xmodule.partitions.tests.test_partitions.TestGetCourseUserPartitions.test_enrollment_track_partition_added`

This test fails intermittently and has been deleted according to the Flaky Test Process in https://github.com/edx/edx-platform/pull/27885.

See docs on how to address flaky tests for why this should be fixed and how to go about it.

• Failed and then passed in https://github.com/edx/edx-platform/pull/27881
• Failure in Jenkins: https://build.testeng.edx.org/job/edx-platform-python-pipeline-pr/31393/testReport/junit/xmodule.xmodule.partitions.tests.test_partitions/TestGetCourseUserPartitions/Run_Tests___commonlib_unit___test_enrollment_track_partition_added/ (no longer accessible)

Related: https://github.com/openedx/edx-platform/issues/35640

Failure output:

Regression
Run Tests / commonlib-unit / xmodule.xmodule.partitions.tests.test_partitions.TestGetCourseUserPartitions.test_enrollment_track_partition_added (from pytest)

Failing for the past 1 build (Since Failed#31393 )
Took 4 ms.
Error Message
AssertionError: assert 2 == 1
  +2
  -1
Stacktrace
self = <xmodule.partitions.tests.test_partitions.TestGetCourseUserPartitions testMethod=test_enrollment_track_partition_added>

    def test_enrollment_track_partition_added(self):
        """
        Test that the dynamic enrollment track scheme is added if there is no conflict with the user partition ID.
        """
        all_partitions = get_all_partitions_for_course(self.course)
>       assert 2 == len(all_partitions)
E       AssertionError: assert 2 == 1
E         +2
E         -1

common/lib/xmodule/xmodule/partitions/tests/test_partitions.py:560: AssertionError

(Previously filed as https://2u-internal.atlassian.net/browse/CR-3732)

Start with common/lib/xmodule/xmodule/partitions/tests/test_partitions.py around the deleted test at line 560, then read PR 27885 and the linked flaky-test guidance. Investigate why get_all_partitions_for_course sometimes returns one partition instead of two, reproduce the intermittent failure if possible, and ensure the enrollment-track partition behavior has stable regression coverage.