fix(langchain-py): upgrade urllib3 to 2.8.0 (#856)

This upgrades `urllib3` (currently 2.7.0) to 2.8.0, which carries the
fix for CVE-2026-97689. The package is present in this repository's
dependency tree; I have not verified that your code reaches the affected
function.

Reference:
[CVE-2026-97689](https://nvd.nist.gov/vuln/detail/CVE-2026-97689)

## What changed
- `integrations/langchain-py/uv.lock`

## Verification
No automated check could be run against this repository, so this change
is unverified beyond review. Please treat it as a suggestion.

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*Automated security fix by [OrbisAI Security](https://orbisappsec.com)*

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Author: anupamme