Fix streaming test to handle /completion response format

The /completion endpoint returns chunks with 'content' directly,
not wrapped in 'choices' array like chat completions endpoint.

Co-Authored-By: Alex Peng <[email protected]>

Author: devin-ai-integration[bot]

tools/server/tests/e2e/test_pipeline_workflows.py

@@ -181,10 +181,8 @@ def test_streaming_pipeline(pipeline_process, e2e_small_model_config):
 
     content = ""
     for chunk in chunks:
-        if chunk.get("choices"):
-            choice = chunk["choices"][0]
-            if "content" in choice:
-                content += choice["content"]
+        if "content" in chunk:
+            content += chunk["content"]
 
     assert len(content) > 0, "Should have generated content"