Keep support for python 3.6 and 3.7

[woutdenolf]

Related to #810

Breaking changes were introduced here: #808

Overview of build issues: #810 (comment)

I'm not sure how to build locally (make build fails because pyyaml_build_config is only added in CI?) so I didn't test this PR.

Alternatively to this PR: nuke 6.0.2rc1 on pypi and drop support for python 3.6 and 3.7

[woutdenolf]

nullcontext was introduced in python 3.7

[woutdenolf]

this f-string syntax was introduced in python 3.8

[nitzmahone]

Yeah, I realized I hadn't yet fixed the metadata to properly signal lack of 3.6 and 3.7 support right after I did 6.0.2rc1. Other than the ability to build the libyaml extension with Cython 3.x, there shouldn't be any "interesting" features or bugfixes in 6.0.2 over 6.0.1, so I'm much more likely to just fix the metadata in a 6.0.2rc2 and yank 6.0.1rc1 at the same time (so 3.6/3.7 users will continue to get 6.0.1 forever).

[PraveenPenguin]

Yeah, I realized I hadn't yet fixed the metadata to properly signal lack of 3.6 and 3.7 support right after I did 6.0.2rc1. Other than the ability to build the libyaml extension with Cython 3.x, there shouldn't be any "interesting" features or bugfixes in 6.0.2 over 6.0.1, so I'm much more likely to just fix the metadata in a 6.0.2rc2 and yank 6.0.1rc1 at the same time (so 3.6/3.7 users will continue to get 6.0.1 forever).

@nitzmahone any outlook on this when we have a fix on this as we are facing an issue due to this while using one framework

avocado-framework/avocado#5975

[nitzmahone]

Now that Python 3.13.0rc1 has been tagged, PyYAML 6.0.2 final should be out within the next several days, at which point I'll yank 6.0.2rc1. For now, just don't install with --pre.

[nitzmahone]

6.0.2 released with corrected python_requires metadata to exclude < 3.8, and the erroneous 6.0.2rc1 has been yanked, so further --pre installs should continue to work on EoL Pythons.

[woutdenolf]

I can confirm this solved the issue. Thanks!