docs: prepare for 0.9.0b4

[henryiii]

After #162, so backends can test the dynamic metadata changes.

[henryiii]

@frostming, @dnicolodi, @pradyunsg, and myself, as backend maintainers: I'm planning to do another beta release on Friday with the metadata changes. I might tackle multi-error reporting (but probably not), otherwise, that will likely end the development cycle for this release. Once we've verified that it works (and I plan to try adding PEP 639 support for scikit-build-core using the beta), we should be ready for a full release, maybe next week. I can roll back any of the changes if needed before then. Most notably, it's now an attribute error to set a value that's not dynamic after you've loaded a pyproject.toml, but if that's an issue for any of the backends, we can make it a warning instead, for instance.

[henryiii]

Also, if any of you have a use for #128, we could add that, I just don't see a way to use it at the moment; it would be useful in the internals, but we lose static typing by wrapping the dict access. It's not useful as the type of from_pyproject, since then mypy won't let you load the result of tomllib into it.

[dnicolodi]

I haven't seen anything that may be problematic for meson-python in the merged PRs. However, I'll be traveling and it is likely that I'll not be able to integrate support for metadata 2.4 or to do integration tests for the next two weeks.

[henryiii]

I don't think there's a rush, unless another backend (that doesn't embed it) needs it quickly. And some people are testing with --pre, so any breakage hopefully will show up after we release the beta.

[henryiii]

FYI, this is stuck with:

Uploading distributions to https://upload.pypi.org/legacy/
Uploading pyproject_metadata-0.9.0b4-py3-none-any.whl
WARNING  Received "502: Bad Gateway"                                            
         Package upload appears to have failed. Retry 1 of 5.                   
Uploading pyproject_metadata-0.9.0b4-py3-none-any.whl
WARNING  Received "502: Bad Gateway"                                            
         Package upload appears to have failed. Retry 2 of 5.                   
Uploading pyproject_metadata-0.9.0b4-py3-none-any.whl
WARNING  Received "502: Bad Gateway"                                            
         Package upload appears to have failed. Retry 3 of 5.                   
Uploading pyproject_metadata-0.9.0b4-py3-none-any.whl
WARNING  Received "502: Bad Gateway"                                            
         Package upload appears to have failed. Retry 4 of 5.                   
Uploading pyproject_metadata-0.9.0b4-py3-none-any.whl
WARNING  Received "502: Bad Gateway"                                            
         Package upload appears to have failed. Retry 5 of 5.                   
WARNING  Error during upload. Retry with the --verbose option for more details. 
ERROR    HTTPError: 502 Bad Gateway from https://upload.pypi.org/legacy/        
         Bad Gateway     

I think PyPI might be at fault here.

[henryiii]

Manually uploaded for now. We can drop attestations: true if we need to make another release before pypa/gh-action-pypi-publish#263 is resolved.