Use the same poetry version as dev and CI

What does this merge request do and why?

We have since upgraded to poetry-1.8.3 and used it in development and CI. This MR ensures we use the same poetry version when building the docker image.

How to set up and validate locally

1. Check out to this merge request's branch.
2. Build the runner docker image and confirm no error.

   docker build --target=runner --tag promptlib-runner:latest .

Merge request checklist

• I've ran the affected pipeline(s) to validate that nothing is broken.
• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.