chore(ci): bring back poetry cache to speed up CI jobs

[bowenliang123]

Checklist:

Important

Please review the checklist below before submitting your pull request.

• Please open an issue before creating a PR or link to an existing issue
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

Description

• as the actions-poetry 3.0.1 fixes the pipx installation problem with python3 on ubuntu 24.04 LTS in fix: ubuntu pipx installation by calling pip from python3 abatilo/actions-poetry#71 , time to revert fix: poetry installation in CI jobs #9336 to bring back poetry cache for faster ci runs
• saving 633 MB network traffic for downloading the Python dependencies and over 60 seconds execution time, in every single CI run

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update, included: Dify Document
• Improvement, including but not limited to code refactoring, performance optimization, and UI/UX improvement
• Dependency upgrade

Testing Instructions

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A
• Test B