db-dtypes release procedure

Checkout main branch

git fetch upstream main
git checkout main
git rebase -i upstream/main

Update version number in setup.py
Update CHANGELOG.md

Commit and push

git commit -m "Release x.x.x"
git push upstream main

Build the package

git clean -xfd
python setup.py register sdist bdist_wheel --universal

Upload to test PyPI

twine upload --repository testpypi dist/*

Try out test PyPI package

pip install --upgrade --index-url https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple db-dtypes

Upload to PyPI
```
twine upload dist/*
```
Tag release on GitHub