Fix auth routing in samples 06/11: api_key -> credential for Azure OpenAI

Both samples passed a bearer token provider via api_key= which caused the
client to route to api.openai.com instead of Azure OpenAI, resulting in
401 Unauthorized. Changed to credential= which correctly triggers Azure
routing and picks up AZURE_OPENAI_ENDPOINT from the environment.

- samples/azure_functions/11_workflow_parallel/function_app.py: 1 fix
- samples/durabletask/06_multi_agent_orchestration_conditionals/worker.py: 2 fixes
- Re-enable 4 parallel workflow tests and 1 conditional branching test

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/packages/durabletask/tests/integration_tests/test_06_dt_multi_agent_orchestration_conditionals.py

@@ -52,7 +52,6 @@ class TestMultiAgentOrchestrationConditionals:
         assert email_agent is not None
         assert email_agent.name == EMAIL_AGENT_NAME
 
-    @pytest.mark.skip(reason="Orchestration fails with RuntimeError (status=Failed, output=None) - not a timeout issue")
     def test_conditional_branching(self):
         """Test that conditional branching works correctly."""
         # Test with obvious spam