test: suppress expected error logs in SSE test (#3886)

Our unit test outputs are filled with all kinds of obscene logs. This
makes it really hard to spot real issues quickly. The problem is that
these logs are necessary to output at the given logging level when the
server is operating normally. It's just that we don't want to see some
of them (especially the noisy ones) during tests.

This PR begins the cleanup. We pytest's caplog fixture to for
suppression.

tests/unit/server/test_sse.py

@@ -5,12 +5,21 @@
 # the root directory of this source tree.
 
 import asyncio
+import logging  # allow-direct-logging
 from unittest.mock import AsyncMock, MagicMock
 
+import pytest
+
 from llama_stack.apis.common.responses import PaginatedResponse
 from llama_stack.core.server.server import create_dynamic_typed_route, create_sse_event, sse_generator
 
 
+@pytest.fixture
+def suppress_sse_errors(caplog):
+    """Suppress expected ERROR logs for tests that deliberately trigger SSE errors"""
+    caplog.set_level(logging.CRITICAL, logger="llama_stack.core.server.server")
+
+
 async def test_sse_generator_basic():
     # An AsyncIterator wrapped in an Awaitable, just like our web methods
     async def async_event_gen():
@@ -70,7 +79,7 @@ async def test_sse_generator_client_disconnected_before_response_starts():
     assert len(seen_events) == 0
 
 
-async def test_sse_generator_error_before_response_starts():
+async def test_sse_generator_error_before_response_starts(suppress_sse_errors):
     # Raise an error before the response starts
     async def async_event_gen():
         raise Exception("Test error")