Rename `master` to `main`?

[hugovk]

To match most of the other https://github.com/python repos.

Instructions: https://github.com/github/renaming#renaming-existing-branches

The branch name isn't referred to in this repo's code.

[sethmlarson]

Agreed, I don't have the privileges to make the edit though :)

[hugovk]

@python/organization-owners Please could you rename the default branch?

[ewdurbin]

Done.

[hugovk]

Thanks!

For those with a fork, you can rename your own default branch to main at https://github.com/YOUR-USERNAME/release-tools/settings

And then run this in your local clone:

git branch -m master main
git fetch origin
git branch -u origin/main main
git remote set-head origin -a

cc @python/release-managers