docs: contribute / integrations code examples update (#19319)
**Description:** Update to make the code examples consistent with the
actual use
**Issue:** Code examples were different from actual use in the LangChain
code
**Dependencies:** Changes on top of
https://github.com/langchain-ai/langchain/pull/19294
Note: If these changes are acceptable, please merge them after
https://github.com/langchain-ai/langchain/pull/19294.
