fix: Upgrade next to fix HTTP deserialization DoS (#11597)
## Summary
Upgrades `next` from 16.1.1 to 16.1.5 in docs/site to fix a high
severity HTTP request deserialization DoS vulnerability.
## Vulnerability Details
- **Package**: next >=16.1.0-canary.0 <16.1.5
- **Issue**: HTTP request deserialization DoS
- **Severity**: High
- **Dependency Path**: docs/site > next
## Changes
- Updated `next` version in `docs/site/package.json` from 16.1.1 to
16.1.5
- Updated `pnpm-lock.yaml` accordingly
Fixes TURBO-5147
