[rid/dp_behavior] Fix misplaced end_test_case

[barroco]

Running the rid/dp_behavior test scenario with multiple observers fails with the error below because of a misplaced end_test_case call. This PR fixes it.

2025-09-02 11:15:54.157 | ERROR    | monitoring.uss_qualifier.suites.suite:_run_test_scenario:176 - Execution error:
  Traceback (most recent call last):
    File "/app/monitoring/uss_qualifier/suites/suite.py", line 158, in _run_test_scenario
      scenario.run(context)
      ~~~~~~~~~~~~^^^^^^^^^
    File "/app/monitoring/uss_qualifier/scenarios/astm/netrid/common/dp_behavior.py", line 141, in run
      self.begin_test_case("Display Provider Behavior")
      ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/app/monitoring/uss_qualifier/scenarios/scenario.py", line 368, in begin_test_case
      self._expect_phase(ScenarioPhase.ReadyForTestCase)
      ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/app/monitoring/uss_qualifier/scenarios/scenario.py", line 320, in _expect_phase
      raise RuntimeError(
          f"Test scenario `{self.me()}` was {self._phase} when {caller} was called (expected {acceptable_phases})"
      )
  RuntimeError: Test scenario `monitoring.uss_qualifier.scenarios.astm.netrid.v22a.dp_behavior.DisplayProviderBehavior` was ScenarioPhase.ReadyForTestStep when begin_test_case was called (expected ReadyForTestCase)