Dependabot can already take the Python version to use from pyproject.toml if it's in Poetry's format (see: https://github.com/dependabot/dependabot-core/blob/main/python/lib/dependabot/python/file_parser/python_requirement_parser.rb#L57), but PEP621 offered a common way to define which version of Python is required using requires-python in pyproject.toml: https://packaging.python.org/en/latest/specifications/declaring-project-metadata/#requires-python

It would be great if Dependabot could support this so we could just maintain it there (currently not using Poetry, so we specify the python version in runtime.txt since we have .python-version in .gitignore to not conflict with pyenv virtualenvs).

This was originally brought up in a comment on another issue:
Based on: #4216 (comment)_

I would like to avoid scope creep on this by just having the lower-bound of Python used (e.g. >=3.11 should use the latest 3.11, not 3.12). The linked issue (#4216) could also solve our use-case since we use pip-compile, but if that's too tricky then at least the requires-python in pyproject.toml would help us.