Bump urllib3 from 2.6.0 to 2.6.3 in /protovalidate/grpc-python/start

Bumps [urllib3](https://github.com/urllib3/urllib3) from 2.6.0 to 2.6.3.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@2.6.0...2.6.3)

---
updated-dependencies:
- dependency-name: urllib3
  dependency-version: 2.6.3
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

protovalidate/grpc-python/start/requirements.txt

@@ -37,7 +37,7 @@ types-protobuf==6.30.2.20250516
 types-python-dateutil==2.9.0.20250516
 types-PyYAML==6.0.12.20250516
 typing_extensions==4.12.2
-urllib3==2.6.0
+urllib3==2.6.3
 v1==0.12.3