test: isolate MCP timeout regression from DNS

tests/tools/test_mcp_tool.py

@@ -656,11 +656,15 @@ async def test_connect_mcp_servers_streamable_http_uses_finite_timeout(
     async def _reachable(_url: str) -> bool:
         return True
 
+    def _validate(_url: str) -> tuple[bool, str]:
+        return True, ""
+
     @asynccontextmanager
     async def _capturing_streamable_http_client(_url: str, http_client=None):
         captured["timeout"] = http_client.timeout
         yield object(), object(), object()
 
+    monkeypatch.setattr(mcp_mod, "validate_url_target", _validate)
     monkeypatch.setattr(mcp_mod, "_probe_http_url", _reachable)
     monkeypatch.setattr(
         sys.modules["mcp.client.streamable_http"],