test(mcp): comment empty except in bridge test cleanup

Address github-code-quality review on PR #2465: explain why the
OSError swallow in pipe teardown is intentional (best-effort
cleanup of a possibly-already-closed fd).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

workspace/tests/test_a2a_mcp_server.py

@@ -456,6 +456,8 @@ async def test_inbox_bridge_emits_channel_notification_to_writer():
         try:
             os.close(read_fd)
         except OSError:
+            # read_fd may already be closed if writer.close() tore down the pair
+            # during teardown — best-effort cleanup, no signal worth surfacing.
             pass