Bump python from 3.12 to 3.13 in /test/environment/grpc

Bumps python from 3.12 to 3.13.

---
updated-dependencies:
- dependency-name: python
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

test/environment/grpc/Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.12
+FROM python:3.13
 
 RUN mkdir -p /usr/src/app
 WORKDIR /usr/src/app