Update testing GitHub Action to check for differences in poetry.lock

It is easy to forget to update poetry.lock file after changing something in the pyproject.toml file. There should be a step in testing workflow that

1. Gets a hash of the lock file right after the checkout and saves into an environment variable
2. Runs poetry update
3. Gets the hash again and compares with the previous hash
4. If results are different, then breaks the workflow.

Acceptance Criteria

• Steps to verify correctness of poetry.lock file is added to testing GitHub Action