tox packaging job fails in CI

Ninguém assumiu esta issue ainda.

E.g. as in https://travis-ci.org/github/matrix-org/python-signedjson/jobs/770347173

```
$ tox
GLOB sdist-make: /home/travis/build/matrix-org/python-signedjson/setup.py
packaging create: /home/travis/build/matrix-org/python-signedjson/.tox/packaging
packaging installdeps: check-manifest
packaging inst: /home/travis/build/matrix-org/python-signedjson/.tox/.tmp/package/1/signedjson-1.1.2.dev6+gde64b47.zip
packaging installed: canonicaljson==1.1.4,cffi==1.14.0,check-manifest==0.41,frozendict==1.2,importlib-metadata==1.6.0,pep517==0.8.2,pycparser==2.20,PyNaCl==1.3.0,signedjson==1.1.2.dev6+gde64b47,simplejson==3.17.0,six==1.14.0,toml==0.10.0,typing-extensions==3.7.4.2,unpaddedbase64==1.1.0,zipp==3.1.0
packaging run-test-pre: PYTHONHASHSEED='2381353217'
packaging run-test: commands[0] | check-manifest
lists of files in version control and sdist do not match!
missing from sdist:
CHANGELOG.md
RELEASING.md
changelog.d
pyproject.toml
suggested MANIFEST.in rules:
include *.md
include *.toml
ERROR: InvocationError for command /home/travis/build/matrix-org/python-signedjson/.tox/packaging/bin/check-manifest (exited with code 1)
___________________________________ summary ____________________________________
ERROR: packaging: commands failed
The command "tox" exited with 1.
Done. Your build exited with 1.
```

Comece executando tox e inspecionando setup.py, a configuração do job de empacotamento e a saída de check-manifest. Confirme por que CHANGELOG.md, RELEASING.md, changelog.d e pyproject.toml estão ausentes da distribuição de código-fonte e, em seguida, verifique se o job de empacotamento é concluído com sucesso com todos os arquivos necessários incluídos.

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