fix(release): change release workflow to use git plugin

The former method of supporting semantic release attempted to use a pull request and automatic merging of the that pull request to commit the changed version numbers to the release branch but this did not commit at the right time and didn't properly work in an automated manner. The new method uses the git plugin for semantic release to accomplish the same goal but at a time that works better for the subsequent semantic release steps and (hopefully) is fully automated.

A key change from prior attempts to use the git plugin is the "persist-credentials: false" argument to the Checkout step. This appears to be necessary for the git plugin to properly use the "sbosnick-bot" personal access token from secrets.SEMRELGH.

This change also refactors the push trigger out of the ci workflow into its own release workflow. The ci workflow is now exclusivly for pull requests.

kettleby / semantic-release-rust

fix(release): change release workflow to use git plugin #19