Fix dependency update GitHub workflow

[nsoranzo]

Follow-up on #16638 , which broke the lint requirement update script:

• Use poetry to generate the pinned typecheck requirements. The generation of the pinned lint requirements needs to remain separate because flake8 requires importlib-metadata 4.2, while the Galaxy's core dependencies depend on importlib-metadata 4.13.
• Install both Python 3.7 and 3.8 in the dependency update workflow to generate both pinned lint requirements (using pip freeze under Python 3.7) and core/dev/typecheck requirements (using poetry under Python 3.8).

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[mvdbeek]

Thank you @nsoranzo!