Consider increasing the minimum Python version

[gotmax23]

antsibull currently supports Python 3.6 and above. I propose increasing the bumping Python version to 3.8. For one thing, the latest Ansible release to support below Python 3.8 (on the controller) was 2.11/4, so antsibull is useless on older Python versions for building new ansible releases. Currently, there are multiple TODO: PY3.8 comments throughout the codebase:

$ rg 'TODO: PY3.8'
antsibull/src/antsibull/build_ansible_commands.py:        # TODO: PY3.8:
antsibull/src/antsibull/build_ansible_commands.py:        # TODO: PY3.8:
antsibull-core/src/antsibull_core/ansible_core.py:                # TODO: PY3.8: while chunk := await response.read(lib_ctx.chunksize):
antsibull-core/src/antsibull_core/dependency_files.py:    # TODO: PY3.8:
antsibull-core/src/antsibull_core/utils/hashing.py:        # TODO: PY3.8: while chunk := await f.read(ctx.chunksize):
antsibull-core/src/antsibull_core/galaxy.py:        # TODO: PY3.8: self.collection_cache: t.Final[t.Optional[str]] = collection_cache
antsibull-core/src/antsibull_core/galaxy.py:                # TODO: PY3.8: We can use t.Final in __init__ instead of cast here.
antsibull-core/src/antsibull_core/galaxy.py:                # TODO: PY3.8: while chunk := await response.content.read(lib_ctx.chunksize):
antsibull-core/src/antsibull_core/galaxy.py:            # TODO: PY3.8: We can use t.Final in __init__ instead of cast here.
antsibull-core/src/antsibull_core/utils/io.py:            # TODO: PY3.8: while chunk := await f.read(lib_ctx.chunksize)

Amongst other improvements, we'd able to take advantage of new type-hinting enhancements from Python 3.9 and 3.10 by using from __future__ import annotations. E.g., t.Dict[str, str] > dict[str, str] and t.Optional[str] -> str | None. (We couldn't use the newer syntax on 3.8 in the pydantic models, but it's fair game everywhere else.)

[gotmax23]

We'd also be able to remove everything except BooleanOptionalAction from https://github.com/ansible-community/antsibull-core/blob/main/src/antsibull_core/compat.py.

[felixfontein]

I thought about this earlier, but never got around to do that yet. Both antsibull and antsibull-changelog can easily go up to 3.8. I would probably stick to 3.8 for now and not use 3.9 though. The advantages of 3.9 are not that big that it's worth annoying devs who still stick to 3.8 for whatever reasons (this is more a problem for antsibull-changelog than for antsibull though).