[ci] put ceiling on graphviz in Python 3.7 jobs

[jameslamb]

Python 3.7 CI jobs are failing with this error:

../../../.local/lib/python3.7/site-packages/lightgbm/compat.py:62: in <module>
    import graphviz  # noqa: F401
../../../miniforge/envs/test-env/lib/python3.7/site-packages/graphviz/__init__.py:31: in <module>
    from .backend import (DOT_BINARY, UNFLATTEN_BINARY,
../../../miniforge/envs/test-env/lib/python3.7/site-packages/graphviz/backend/__init__.py:5: in <module>
    from .mixins import Render, Pipe, Unflatten, View
../../../miniforge/envs/test-env/lib/python3.7/site-packages/graphviz/backend/mixins.py:8: in <module>
    from . import piping
../../../miniforge/envs/test-env/lib/python3.7/site-packages/graphviz/backend/piping.py:5: in <module>
    from .. import _tools
E     File "/Users/runner/miniforge/envs/test-env/lib/python3.7/site-packages/graphviz/_tools.py", line 23
E       def attach(object: typing.Any, /, name: str) -> typing.Callable:
E                                      ^
E   SyntaxError: invalid syntax

Example recent build from master: (build link).

python-graphviz has a floor of python>=3.8 since xflr6/graphviz#202, but I guess that hasn't extended to the conda-forge package. That results in a newer version of python-graphviz being pulled into a Python 3.7 environment which contains invalid syntax for Python 3.7.

This PR proposes putting a ceiling on python-graphviz in LightGBM's Python 3.7 CI jobs.

Notes for Reviewers

Looks like this is the result of the latest python-graphviz release on conda-forge about 4 hours ago: conda-forge/python-graphviz-feedstock#55.

I don't think conda-forge will be interested in a repodata patch to prevent this from happening, so I'm not planning to propose one. Based on this evidence:

• [ci] Python 3.7 CI jobs broken by zipp release #5969 (comment)
• https://conda.io/projects/conda/en/latest/user-guide/tasks/manage-python.html
  • "Conda supports Python 3.8, 3.9, 3.10, 3.11 and 3.12."
• Pin python>=3.8 for zipp 3.16.0 conda-forge/conda-forge-repodata-patches-feedstock#478 (review)

I did put up conda-forge/python-graphviz-feedstock#56 proposing adding a python>=3.8 floor on conda-forge, so maybe if that's merged we could eventually remove this ceiling in CI scripts.

If this ceiling on python-graphviz causes problems in the future, I'd support turning off the plotting tests for Python 3.7 environments.

[jameslamb]

absolutely BRUTAL week for our CI 😭

[borchero]

Thanks!

[borchero]

Let's go? 😄 this should unblock a lot of CI 👀