Python CI: pin mypy version to avoid CI failure due to new release

[HonahX]

Mypy did a new release 1.16.1 and it cause our CI to fail for about 20 minutes due to missing wheel (upload not completed)

 | Unable to find installation candidates for mypy (1.16.1)
    | 
    | This is likely not a Poetry issue.
    | 
    |   - 14 candidate(s) were identified for the package
    |   - 14 wheel(s) were skipped as your project's environment does not support the identified abi tags
    | 
    | Solutions:
    | Make sure the lockfile is up-to-date. You can try one of the following;
    | 
    |     1. Regenerate lockfile: poetry lock --no-cache --regenerate
    |     2. Update package     : poetry update --no-cache mypy
    | 
    | If neither works, please first check to verify that the mypy has published wheels available from your configured source that are compatible with your environment- ie. operating system, architecture (x86_64, arm64 etc.), python interpreter.
    | 

This PR temporarily restrict the mypy version to avoid the similar issue.

We may consider bring poetry.lock back to git tracking so we won't automatically update test dependencies all the time

[XJDKC]

I remember this file is generated, should we modify this file considering this?

[eric-maynard]

It's now not supposed to be generated anymore

[HonahX]

This file is no longer auto-generated because we also have CLI codes and test which needs additional dependencies/configs. We are currently manually managing the pyproject.toml