ci: add publish script to changesets workflow

[phoenix-server]

Problem

The changesets/action was missing a publish script, so when a release PR was merged, it logged:

Not publishing because no publish script found.

No tag or GitHub release was ever created automatically.

Fix

Add publish: pnpm run changeset:publish to the action. The changeset:publish script already exists in package.json and .changeset/config.json has privatePackages: { tag: true }, so this will create git tags and GitHub releases without publishing to npm.

[changeset-bot]

⚠️ No Changeset found

Latest commit: a7710c9

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR