* RELEASE: update to v0.12
* add myst_deprecations notification to CHANGELOG
* update CHANGELOG
* fix myst-nb intersphinx link
* FIX: broken links to myst-nb due to https://github.com/executablebooks/MyST-NB/pull/365
* add thanks to contributors
* update thanks
* Sphinx 4 in github actions
* upgrade win, os x tests to python=3.8; and pypi publish workflow
* update cache key to be more generic
* use a simple test matrix to set python-version
* FIX: add $
Co-authored-by: Chris Holdgraf <[email protected]>
