Add note about mypy

Author: Carreau

jupyter_server/services/kernels/kernelmanager.py

@@ -220,7 +220,7 @@ async def _async_start_kernel(
             if path is not None:
                 kwargs["cwd"] = self.cwd_for_path(path, env=kwargs.get("env", {}))
             if kernel_id is not None:
-                assert kernel_id is not None
+                assert kernel_id is not None, "Never Fail, but necessary for mypy "
                 kwargs["kernel_id"] = kernel_id
             kernel_id = await self.pinned_superclass._async_start_kernel(self, **kwargs)
             self._kernel_connections[kernel_id] = 0