After cloning the repository locally, run:
composer install
On GitHub, create a new release. Set the tag and release title to the semantic version, but prepend the letter v. For example, if releasing version 1.1.1, the tag and release title should be v1.1.1. Leave target set to main and add any release notes to the description field.
Hit 'Publish release' to finalize the release. This will automatically update Packagist with the latest version.