Fix CI triggers: Only run Python tests when Python files change

[neubig]

This PR fixes the CI configuration to only run Python tests when Python files are changed.

Currently, the Python tests are running on all PRs, even when only frontend files are changed. This causes unnecessary CI runs and potential failures due to missing frontend dependencies in the Python test environment.

Changes:

• Added paths filter to the Python test workflow to only run when Python files or related files are changed
• Files that trigger Python tests:
  • openhands/**
  • agenthub/**
  • evaluation/**
  • tests/**
  • pyproject.toml
  • poetry.lock
  • .github/workflows/py-unit-tests.yml

This change will make the CI more efficient and avoid false failures.

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:840ebf7-nikolaik   --name openhands-app-840ebf7   docker.all-hands.dev/all-hands-ai/openhands:840ebf7