test(langchain): cover runtime recursion limit override in create_agent (#36376)

Extends the existing unit test for to verify that a per-invoke override
is visible inside the tool runtime config. This keeps the coverage in
the existing fake-model end-to-end test and exercises both the default
config path and the override path in one place.

Created with [Deep Agents
CLI](https://docs.langchain.com/oss/python/deepagents/cli/overview)
using gpt-5.4 (provider: openai).