Release automation: create sdist on CI

[hugovk]

Next step of automation for #7390.

This creates the sdist on the CI:

• No need to create it locally
• Safer to build on the CI than a potentially compromised local machine
• Better reproduciblity

The sdist is added as a new job to the wheels.yml workflow and added to the same GitHub artifact as the wheels, which I've renamed from wheel to dist.

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We'll probably want to rename wheels.yml to something not specific to wheels (because we build a source distribution as well), I was thinking about renaming deploy.yml once we start publishing to PyPI, but open to renaming now as well.