Releasing a new version of Primer CSS 🎉

Prepare the release (in `primer/css`)

The release process is automated by changesets. After you familiarize yourself with how they work. We use an action workflow integrated in ci.

Visit the pull requests page and find the latest Release tracking pr from primer-css. If there isn't one, we'll need to build the next release by merging in PRs with changeset files.

Create a new branch in the github/github repo, name it primer-<version>.
Update the Primer CSS version to the published release candidate with:
```
bin/npm install @primer/css@<version>-rc.<sha>
```
Then commit and push the changes to package.json, package-lock.json, LICENSE and vendor/npm.
If you need to make changes to github/github due to the Primer CSS release, do them in a branch and merge that into your release branch after testing.
Add or re-request reviewers and fix any breaking tests.
Test on review-lab.

If the release PR got approved and you've done necessary testing, merge it.

After tests run, the docs site will be deployed and @primer/css will be published with your changes to the latest dist-tag. You can check npm to see if actions has finished.
Done! 🎉

Install the latest published version in the same primer-<version> branch created earlier with:
```
bin/npm install @primer/css@<version>
```
Then commit and push the changes to package.json, package-lock.json, LICENSE and vendor/npm.
Fix any breaking tests.
Deploy! 🚀